Bolt torque chart and calculator.

Bolt torque chart

A manufacturer's torque specification always overrides this chart. The values here are generic figures for plain steel bolts computed from clamp load and a typical nut factor. Where a service manual, a drawing, a flange or structural bolting procedure, or the fastener maker gives a torque or a torque-angle sequence, use that, not this page.

Inch (UNC / UNF) Metric (ISO coarse)

75% of proof (reusable) 90% of proof (one-time, permanent)

Grade or class Grade 2Grade 5Grade 8

Find a size

Size	TPI	Stress area (in²)	Grade	Proof load (lb)	Clamp load (lb)	Dry K 0.20 (lb·ft)	Dry (N·m)	Lubricated K 0.15 (lb·ft)	Lubricated (N·m)
1/4-20 UNC	20	0.0318	Grade 5	2,705	2,029	101 lb·in	11.5	76 lb·in	8.6
1/4-28 UNF	28	0.0364	Grade 5	3,092	2,319	116 lb·in	13.1	87 lb·in	9.8
5/16-18 UNC	18	0.0524	Grade 5	4,457	3,342	209 lb·in	24	157 lb·in	17.7
5/16-24 UNF	24	0.0581	Grade 5	4,936	3,702	231 lb·in	26	174 lb·in	19.6
3/8-16 UNC	16	0.0775	Grade 5	6,587	4,940	31	42	23	31
3/8-24 UNF	24	0.0878	Grade 5	7,465	5,599	35	47	26	36
7/16-14 UNC	14	0.1063	Grade 5	9,036	6,777	49	67	37	50
7/16-20 UNF	20	0.1187	Grade 5	10,091	7,568	55	75	41	56
1/2-13 UNC	13	0.1419	Grade 5	12,061	9,046	75	102	57	77
1/2-20 UNF	20	0.1600	Grade 5	13,596	10,197	85	115	64	86
9/16-12 UNC	12	0.1819	Grade 5	15,465	11,599	109	147	82	111
9/16-18 UNF	18	0.2030	Grade 5	17,253	12,940	121	164	91	123
5/8-11 UNC	11	0.2260	Grade 5	19,210	14,408	150	203	113	153
5/8-18 UNF	18	0.2560	Grade 5	21,756	16,317	170	230	127	173
3/4-10 UNC	10	0.3345	Grade 5	28,429	21,322	267	361	200	271
3/4-16 UNF	16	0.3730	Grade 5	31,702	23,776	297	403	223	302
7/8-9 UNC	9	0.4617	Grade 5	39,247	29,436	429	582	322	437
7/8-14 UNF	14	0.5095	Grade 5	43,305	32,479	474	642	355	482
1-8 UNC	8	0.6058	Grade 5	51,488	38,616	644	873	483	654
1-12 UNF	12	0.6630	Grade 5	56,359	42,269	704	955	528	716
1-1/8-7 UNC	7	0.7633	Grade 5	56,482	42,362	794	1,077	596	808
1-1/4-7 UNC	7	0.9691	Grade 5	71,714	53,786	1,121	1,519	840	1,139
1-1/2-6 UNC	6	1.4053	Grade 5	103,989	77,991	1,950	2,644	1,462	1,983

Stress area is the tensile stress area of the thread. Proof load is proof stress times stress area, using SAE J429 proof stresses for Grades 2, 5 and 8 and ISO 898-1 proof stresses for classes 8.8, 10.9 and 12.9. Clamp load is the chosen share of proof load. Torque is T = K × d × F with K = 0.20 for plain dry steel and K = 0.15 for lightly lubricated or zinc-plated fasteners; for 1/4 and 5/16 in the inch torque is shown in lb·in. Every value is computed, not copied from a chart, and the real nut factor for your bolt, nut and lubricant can differ from these typical figures by a wide margin.

Torque calculator

Inch (TPI, ksi) Metric (pitch, MPa)

Dry, K 0.20 Plated or light oil, K 0.15 Well lubricated, K 0.12

75% of proof 90% of proof

Nominal diameter (in)

Threads per inch

Grade or class preset Grade 2Grade 5Grade 8Custom proof stress

Proof stress (ksi)

Nut factor K

Clamp load (% of proof)

Recalculate Print chart Reset

75.4 lb·ftTorque, 905 lb·in

102.2 N·mTorque

9,046 lbClamp load, 75% of proof

12,061 lbProof load

0.1419 in²Tensile stress area

1/2-13 UNC Grade 5, dry, tightened to 75% of proof load: 75 lb·ft (102 N·m). The same bolt zinc-plated or lightly oiled (K 0.15) takes 57 lb·ft for the same clamp load, and well lubricated (K 0.12) 45 lb·ft.

Stress area As = 0.7854 × (D − 0.9743 / n)² = 0.7854 × (0.5000 − 0.9743 / 13)² = 0.7854 × 0.4251² = 0.1419 in² Proof load Fp = proof stress × As = 85,000 psi × 0.1419 in² = 12,061 lb Clamp load F = 75% × Fp = 9,046 lb Torque T = K × d × F = 0.20 × 0.5000 in × 9,046 lb = 904.6 lb·in = 904.6 / 12 = 75.4 lb·ft = 102.2 N·m

01What torque is doing: clamp load, preload and why torque is only a proxy

A bolt does its job by stretching. Tightening the nut pulls the bolt slightly longer, the bolt pulls back like a stiff spring, and that pull squeezes the parts together. The squeeze is the clamp load, also called preload. It is the clamp load, not the torque, that keeps a coupling half from working loose, a bearing cap from fretting, a cylinder head from lifting off its gasket or a wheel from moving on its hub. A properly preloaded joint carries most of an external load through the clamped faces, and the bolt itself sees only a small change in tension. An under-preloaded joint lets the parts separate under load, the bolt takes the whole cycle, and it fatigues or the nut backs off.

Nobody on the shop floor can measure bolt tension directly with the tools at hand, so torque stands in for it. Torque is easy to measure with a wrench, and for a given bolt it is roughly proportional to the tension it produces. The problem is the word roughly. Most of the torque you apply is spent overcoming friction, under the nut face and in the threads, and only a small share goes into stretching the bolt. Change the friction, by oiling the threads, by plating, by a burr, by a washer that is rougher or smoother than the last one, and the same torque gives a different clamp load. That is why the chart carries separate dry and lubricated columns, why the calculator asks for a nut factor, and why a manufacturer's figure for a specific fastener in a specific joint beats any generic chart.

Two decisions sit behind every row. The first is how much of the bolt's strength to use. The usual target for a joint that will be disassembled again is a clamp load of about 75% of the proof load, which leaves a margin for the scatter in friction; a permanent joint that will not be reused can go to about 90%. The second is what friction to assume, which is the nut factor. Everything else is arithmetic.

02The formula: T = K × d × F, with the stress area and one full worked example

Torque. T = K × d × F, where T is the tightening torque, K is the nut factor (a dimensionless friction coefficient for the whole assembly), d is the nominal bolt diameter and F is the target clamp load. In inch units, d in inches and F in pounds give T in lb·in; divide by 12 for lb·ft. In metric units, d in metres and F in newtons give T in N·m. One lb·ft is 1.3558 N·m; one lb·in is 0.11298 N·m.

Clamp load. F = pct × proof load, with 75% for a reusable joint and 90% for a one-time, permanent one. Proof load = proof stress × tensile stress area. Proof stress is the stress a bolt can carry without a permanent set, published by grade in SAE J429 for inch bolts and by property class in ISO 898-1 for metric bolts.

Tensile stress area. The load-bearing cross-section of a thread is smaller than a circle at the nominal diameter and larger than one at the minor diameter. The standards define it as As = 0.7854 × (D − 0.9743 / n)² square inches for inch threads, where D is the nominal diameter and n the threads per inch, and As = 0.7854 × (D − 0.9382 × P)² square millimetres for metric threads, where P is the pitch in millimetres. The 0.7854 is π/4.

Worked example: 1/2-13 UNC, Grade 5, dry, 75% of proof (the calculator's default)

Stress area: As = 0.7854 × (0.5000 − 0.9743 / 13)² = 0.7854 × 0.4251² = 0.1419 in². Proof load: Grade 5 proof stress is 85 ksi for 1/4 to 1 in, so Fp = 85,000 × 0.1419 = 12,061 lb. Clamp load: F = 0.75 × 12,061 = 9,046 lb. Torque: T = 0.20 × 0.5000 × 9,046 = 905 lb·in = 75.4 lb·ft = 102.2 N·m. Charts built the same way list 1/2-13 Grade 5 dry in the mid-70s lb·ft, and now you know where the number comes from.

Run backwards, the formula tells you what a wrench setting actually does: F = T / (K × d). A 1/2-13 bolt torqued to 60 lb·ft (720 lb·in) dry gives 720 / (0.20 × 0.5) = 7,200 lb of clamp load, about 60% of a Grade 5 proof load but 92% of a Grade 2 proof load (7,804 lb), well past the 75% target for the Grade 2 bolt and with almost no margin before it yields.

03The nut factor K and why lubrication matters so much

K rolls every source of friction in the joint into one number: thread friction, friction under the nut or bolt head, the thread helix angle, the finish, the washer, the lubricant and how many times the fastener has been tightened before. The typical textbook values, and the ones this page uses, are 0.20 for plain steel, dry, as received; 0.15 for zinc-plated fasteners or plain steel with a light film of oil; and 0.12 for well-lubricated or waxed fasteners, including many thread compounds. They are typical, not measured. Published test results for supposedly identical dry steel bolts spread widely on either side of 0.20, and anti-seize compounds and moly lubricants can push K well below 0.12. The only way to know K for a particular bolt, nut, washer and lubricant is to measure it, which is what fastener makers and the writers of service manuals do before they print a torque.

Because torque is proportional to K, the effect is large and it runs both ways. The 1/2-13 Grade 5 bolt from the example needs 75 lb·ft dry (K 0.20), 57 lb·ft zinc-plated or lightly oiled (K 0.15) and 45 lb·ft well lubricated (K 0.12), all for the same 9,046 lb clamp load. Put the dry figure of 75 lb·ft on the well-lubricated bolt and the clamp load rises by the ratio 0.20 / 0.12, to about 125% of proof load: the bolt yields, and it may snap or strip while you are still pulling on the wrench. Put the lubricated figure on a dry bolt and you get 60% of the intended clamp, which is a joint that will loosen.

So decide the lubrication state first, then read the torque, and make sure the two match on the day. If the manual says dry, clean the threads and keep oil off them; if it says lubricated, it usually names the lubricant, and a different one changes K. When a joint has been apart before, the threads are neither new nor clean, and the real K has moved from whatever it was the first time. A calibrated torque wrench does not fix any of this; it measures torque very well, and torque is only the proxy.

04Grade and class markings, and proof versus tensile strength

Inch bolts (SAE J429). The grade is shown by radial lines on the head. No marks means Grade 2, a low-carbon steel bolt: proof stress 55 ksi for 1/4 to 3/4 in and 33 ksi for larger sizes up to 1-1/2 in, tensile 74 ksi in the smaller range. Three radial lines, spaced 120 degrees apart, mean Grade 5, a quenched and tempered medium-carbon steel bolt: proof 85 ksi for 1/4 to 1 in and 74 ksi above 1 in, tensile 120 ksi. Six radial lines, 60 degrees apart, mean Grade 8, a quenched and tempered alloy steel bolt: proof 120 ksi and tensile 150 ksi across 1/4 to 1-1/2 in. The manufacturer's identification mark is stamped on the head as well. A bolt with no marks and no maker's mark is of unknown strength and should be treated as no better than Grade 2.

Metric bolts (ISO 898-1). The property class is stamped on the head as a number such as 8.8, 10.9 or 12.9; ISO 898-1 requires the marking on hexagon bolts and screws of class 8.8 and higher from M5 up. The class reads as two numbers. The first is the nominal tensile strength in hundreds of megapascals: 8 means 800 MPa, 10 means 1000, 12 means 1200. The second, multiplied by the first, gives the nominal yield strength as a tenth of the tensile: 8.8 is 0.8 × 800 = 640 MPa yield, 10.9 is 0.9 × 1000 = 900, 12.9 is 0.9 × 1200 = 1080. The proof stresses ISO 898-1 lists, and the ones this page uses, sit just under yield: 580 MPa for class 8.8 at M16 and below and 600 MPa above M16, 830 MPa for class 10.9 and 970 MPa for class 12.9. Class 8.8 is roughly equivalent to Grade 5 and class 10.9 to Grade 8, but the diameters, threads and stress areas differ, so the torques are not interchangeable.

Proof, yield and tensile. Tensile strength is the stress at which the bolt breaks. Yield is where it starts to stretch permanently. Proof stress is a little below yield: the bolt is loaded to it in the acceptance test and must show no permanent set. Torque charts and the calculator work from proof, because the target is a bolt that springs back when the joint is unloaded. Use tensile by mistake and the numbers inflate: a 1/2-13 Grade 8 bolt at 75% of proof (120 ksi) needs 106 lb·ft dry, but 75% of tensile (150 ksi) would call for 133 lb·ft and a clamp load of 94% of proof, which leaves no margin at all for the scatter in K: a slightly slick thread and the bolt is past yield.

The nut has to match. A Grade 8 bolt with a low-grade nut strips the nut before the bolt reaches its clamp load; SAE J995 grades hex nuts (Grade 2, 5 and 8) and ISO 898-2 sets metric nut classes (8, 10, 12) to pair with the bolt classes. Washers matter too, since a soft washer that embeds under the nut face loses preload after the wrench comes off.

05When a generic chart must not be used

The manufacturer's specification always overrides this chart. The chart is for plain steel bolts in ordinary joints where nobody has published a figure. In each of the situations below, someone has, and the chart is the wrong tool.

• Torque-to-yield and torque-angle fasteners. Cylinder head bolts, main and rod bolts, flywheel bolts and many driveline fasteners on 421A equipment are tightened to a seating torque and then turned a specified angle, taking the bolt past yield on purpose. The angle, not the torque, sets the clamp load, and the bolt is a one-use part. Follow the service manual's sequence and replace the bolts it says to replace.
• Service manual torque specifications (421A). Every engine, transmission, axle, final drive, hydraulic component and attachment on heavy equipment has a published torque, often with a tightening sequence, a stated lubricant and a re-torque interval. Those figures were measured on that joint with that fastener. Use them.
• Flange bolting. Gasketed pipe and vessel flanges are tightened to a bolt stress chosen for the gasket, in a cross pattern in several passes, with a specified lubricant. Plant bolting procedures based on ASME PCC-1 or the gasket maker's data give the numbers; a generic bolt chart does not know the gasket exists.
• Structural bolting. High-strength structural bolts (ASTM F3125 grades A325 and A490, and their metric equivalents) are installed by turn-of-nut, tension-control bolts, direct tension indicators or calibrated wrench under the structural code (CSA S16 in Canada) and the RCSC specification. A325 is not Grade 5, even though the strengths are close, and it is not tightened from this chart.
• Wheel nuts and hub fasteners. Wheel nut torque is set by the wheel and equipment manufacturer for the stud, nut, rim and hub design, tightened in a star pattern and re-checked after a short period of service. Both under-torque and over-torque have put wheels on the road.
• Bolts threaded into aluminium, cast iron or thin material. The internal thread is weaker than the bolt, so the joint fails by stripping long before the bolt reaches proof load. The chart assumes a nut, or a tapped hole in steel with full engagement. Use the manufacturer's figure or a value based on the parent material and thread engagement.
• Prevailing-torque lock nuts and thread-locking compounds. A nylon-insert or all-metal lock nut resists turning before it seats. The chart value is the torque above that running resistance, so either add the measured prevailing torque or use the nut maker's installation torque. Anaerobic thread lockers also change friction.
• Stainless, brass, bronze and other non-steel fasteners, and anything hot. Different strengths, different friction, and stainless galls. Use the fastener maker's data.

If a drawing, manual or procedure gives a torque, the chart is a way to check that the number is plausible, not a substitute for it.

06Worked examples

Each example is computed by the same arithmetic as the chart. Proof stresses are the SAE J429 and ISO 898-1 figures listed above; K is 0.20 dry, 0.15 plated or lightly oiled, 0.12 well lubricated.

Example 1: 3/8-16 UNC, Grade 5, dry

3/8-16 UNC, Grade 5 (85 ksi), dry, K 0.20, 75% of proof. Stress area = 0.7854 × (0.3750 − 0.9743 / 16)² = 0.0775 in². Proof load = 85 ksi × 0.0775 = 6,587 lb. Clamp load = 75% × 6,587 = 4,940 lb. Torque = 0.20 × 0.3750 × 4,940 = 370 lb·in = 31 lb·ft (42 N·m).

Example 2: M12 × 1.75, class 10.9, dry

M12 × 1.75, class 10.9 (830 MPa), dry, K 0.20, 75% of proof. Stress area = 0.7854 × (12 − 0.9382 × 1.75)² = 84.3 mm². Proof load = 830 MPa × 84.3 = 69,941 N. Clamp load = 75% × 69,941 = 52,456 N. Torque = 0.20 × 0.012 m × 52,456 N = 126 N·m (93 lb·ft).

Example 3: 3/4-10 UNC, Grade 8, dry and well lubricated

3/4-10 UNC, Grade 8 (120 ksi), dry, K 0.20, 75% of proof. Stress area = 0.7854 × (0.7500 − 0.9743 / 10)² = 0.3345 in². Proof load = 120 ksi × 0.3345 = 40,135 lb. Clamp load = 75% × 40,135 = 30,101 lb. Torque = 0.20 × 0.7500 × 30,101 = 4,515 lb·in = 376 lb·ft (510 N·m).

The same bolt with the threads and nut face well lubricated, K 0.12: T = 0.12 × 0.7500 × 30,101 = 2,709 lb·in = 226 lb·ft (306 N·m). Same clamp load, 40% less torque. Tighten the lubricated bolt to the dry figure of 376 lb·ft and the clamp load would reach about 125% of proof.

Example 4: M20 × 2.5, class 8.8, zinc-plated, permanent joint at 90% of proof

M20 × 2.5, class 8.8 (600 MPa above M16), zinc-plated, K 0.15, 90% of proof. Stress area = 0.7854 × (20 − 0.9382 × 2.5)² = 244.8 mm². Proof load = 600 MPa × 244.8 = 146,877 N. Clamp load = 90% × 146,877 = 132,189 N. Torque = 0.15 × 0.020 m × 132,189 N = 397 N·m (292 lb·ft).

At the usual 75% for a reusable joint the same bolt takes 330 N·m (244 lb·ft). Note the proof stress: ISO 898-1 gives class 8.8 a proof stress of 580 MPa at M16 and below but 600 MPa above M16, so an M16 × 2 class 8.8 is worked at 580 MPa and this M20 at 600 MPa.

Example 5: 1-8 UNC, Grade 8, dry

1-8 UNC, Grade 8 (120 ksi), dry, K 0.20, 75% of proof. Stress area = 0.7854 × (1.0000 − 0.9743 / 8)² = 0.6057 in². Proof load = 120 ksi × 0.6057 = 72,689 lb. Clamp load = 75% × 72,689 = 54,517 lb. Torque = 0.20 × 1.0000 × 54,517 = 10,903 lb·in = 909 lb·ft (1,232 N·m).

That is more than most hand torque wrenches read, which is why large bolting is done with multipliers, hydraulic wrenches or bolt tensioners, and why a 1 in Grade 8 bolt at 75% of proof carries about 6 times the clamp load of the 1/2-13 Grade 5 in the first example.

07Common mistakes

• lb·ft and lb·in. Twelve times apart. A 1/2-13 Grade 5 bolt wants about 75 lb·ft, which is 905 lb·in; set a lb·in wrench to 75 and the bolt is barely snug, set a lb·ft wrench to a lb·in figure and it breaks. Small fasteners are usually specified in lb·in or N·m, large ones in lb·ft or N·m. Read the unit on the wrench and on the spec every time. The N·m conversions are 1 lb·ft = 1.356 N·m and 1 lb·in = 0.113 N·m.
• Using tensile strength instead of proof. Proof is the working limit; tensile is the breaking stress. Computing clamp load from tensile overstates the torque by the ratio of the two: 41% for Grade 5 (120 over 85 ksi) and 25% for Grade 8 (150 over 120 ksi), which wipes out the margin the 75% target is there to provide.
• Dry K on a lubricated bolt. Anti-seize on the threads and a dry-chart torque is the classic way to snap a bolt or strip a thread. Match the torque to the lubrication state, and if the manual says dry, keep it dry.
• Torquing the bolt head instead of the nut. The K values here assume the nut is turned against a washer face. Turning the bolt head instead changes which surfaces rub, and with a long bolt some of the torque is absorbed in twisting the shank. Where the manual says torque the nut, torque the nut; where you must turn the head, expect a different clamp load for the same reading and use the manufacturer's figure if one exists.
• Reusing torque-to-yield bolts. A bolt that was tightened past yield has stretched permanently and will not reach its designed clamp load again. Head bolts and other TTY fasteners are replaced, not reused, and the manual will say so.
• Wrong grade for the size rule. Proof stress steps down with diameter for Grade 2 (over 3/4 in) and Grade 5 (over 1 in), and class 8.8 steps up above M16. A 1-1/8-7 Grade 5 bolt is worked at 74 ksi, not 85. The chart and the calculator presets apply the rule automatically; a figure copied across sizes does not.
• Trusting the reading on a damaged or dirty thread. Burrs, rust, paint and a cross-threaded start all raise friction, so the wrench clicks early and the clamp load is low. Chase the thread, clean it, run the nut down by hand first.
• Skipping the pattern and the passes. A multi-bolt joint tightened one bolt to full torque at a time ends up with uneven clamp and a warped part. Snug all, then bring up in steps in a cross or spiral pattern, and finish with a final pass at full torque.
• One-pull on a click wrench. Pull smoothly to the click and stop; a second yank after the click over-torques. Store the wrench wound down and have it calibrated.

08What the 433A and 421A exams expect

433A Industrial Mechanic (Millwright). Fasteners sit in Block A, common occupational skills, which our 433A exam guide gives as 25 of the exam's 135 questions. The guide lists fastening and retaining devices among the sub-tasks of routine trade tasks, the largest task in that block at 26 per cent of it, alongside fabricating a work piece, lubrication, levelling and material identification; the block's tools and equipment task (21 per cent) covers hand and portable power tools, which is where a torque wrench and a multiplier belong. The larger use of torque is in Block C, mechanical power transmission components and systems, the biggest block at 32 questions, where every equipment task has an installs and a repairs sub-task: bolting down a motor, a bearing housing, a coupling half, a gearbox. A question in either block can ask what a bolt grade marking means, which K to use, why lubricated and dry torques differ, or why a joint came loose.

The guide reports that the 433A formula sheet provided with the exam covers rigging, rpm from cutting speed, alignment shims, thermal expansion, areas and volumes, gear pass frequency and force from pressure and area, and that the acronym list includes tpi. Neither T = K × d × F nor the stress-area formula is on that sheet, so a torque question is either recall (which grade, which marking, dry versus lubricated) or a calculation with the numbers and the formula in the stem. The guide also gives the question mix as 30 to 40 per cent knowledge and recall and 40 to 50 per cent procedural and application, which the Red Seal Exam Preparation Guide says may include calculations.

421A Heavy Duty Equipment Technician. Our 421A exam guide puts fasteners and sealing materials in Block A, common occupational skills, under performs routine work practices (34 per cent of the block), and reports that the Red Seal Program's exam information page assigns 3 of the block's 10 questions to routine work practices and 4 to tools and equipment. Torque then runs through the rest of the exam without being named: base engines and lubrication systems in Block B (head bolts, main and rod bolts, torque-to-yield and torque-angle procedures), wheel assemblies in Block C (wheel nut torque and re-torque), and drive axles, final drives and drivelines in Block E. The guide gives the 421A mix as 5 to 15 per cent recall, 45 to 55 per cent procedural and 35 to 45 per cent critical thinking, so expect the torque question to be a procedure (the sequence, the lubricant, the angle, when a bolt is replaced) or a diagnosis (a loose wheel, a leaking head gasket, a sheared bolt) rather than a chart lookup.

For both trades the answer the exam wants is the one the standard and the service manual give. Know the formula and the reasoning here so you can check a figure and explain why lubrication or grade changes it, and know that the manufacturer's specification is the number to use. The free 433A questions and free 421A questions include fastener items in the exam's format.

09Sources

• Red Seal Program: Industrial Mechanic (Millwright) trade page the trade the 433A exam certifies, the occupational standard editions, and the link to the exam information page with the block breakdown, formula sheet and acronym list.
• Red Seal Program: Heavy Duty Equipment Technician trade page the trade the 421A exam certifies and its Red Seal Occupational Standard, which lists fasteners and sealing materials under routine work practices.
• SAE J429: Mechanical and Material Requirements for Externally Threaded Fasteners the standard that sets the proof and tensile strengths and head markings of Grade 2, 5 and 8 inch bolts; the proof stresses used here are 55/33 ksi, 85/74 ksi and 120 ksi as listed above. The metric classes 8.8, 10.9 and 12.9 are defined in ISO 898-1 (mechanical properties of fasteners made of carbon steel and alloy steel, bolts, screws and studs), with proof stresses of 580/600, 830 and 970 MPa. Both standards are copyrighted and neither is reproduced; every torque on this page is computed from those proof stresses, the stress-area formulas and T = K × d × F.
• TicketPrep: 433A Industrial Mechanic (Millwright) Red Seal exam guide the block and task breakdown, the question-type mix, and the formula sheet and acronym list provided at the sitting.
• TicketPrep: 421A Heavy Duty Equipment Technician Red Seal exam guide the block and task breakdown, the per-task question counts in Block A, and the question-type mix.

10Questions people ask

What is the torque for a 1/2-13 Grade 5 bolt?

About 75 lb-ft (102 N-m) dry, for a clamp load of 75% of proof load. That is computed: the stress area is 0.1419 sq in, the proof load at 85 ksi is 12,061 lb, 75% of it is 9,046 lb, and T = 0.20 x 0.5 x 9,046 = 905 lb-in. Zinc-plated or lightly oiled (K 0.15) it is about 57 lb-ft; well lubricated (K 0.12) about 45 lb-ft. A manufacturer's specification for the joint overrides these.

What is the torque for an M12 class 10.9 bolt?

About 126 N-m (93 lb-ft) dry at 75% of proof. M12 x 1.75 has a stress area of 84.3 sq mm; at the ISO 898-1 proof stress of 830 MPa the proof load is 69.9 kN, 75% is 52.5 kN, and T = 0.20 x 0.012 x 52,456 N. Lightly lubricated or plated it is about 94 N-m. Use the service manual's figure where one exists.

Why is the lubricated torque so much lower than the dry torque?

Because most of the torque goes into friction, not bolt stretch. T = K x d x F, and K drops from about 0.20 dry to about 0.15 plated or oiled and 0.12 well lubricated, so the torque for the same clamp load drops in the same proportion. Applying a dry torque to a lubricated bolt raises the clamp load by the ratio of the two K values, which for 0.20 over 0.12 takes a 75% of proof target to about 125% of proof, past yield.

How do I read bolt grade markings?

Inch bolts to SAE J429: no radial lines on the head is Grade 2, three radial lines is Grade 5, six radial lines is Grade 8; the maker's mark is also stamped. Metric bolts to ISO 898-1 carry the property class as a number on the head: 8.8, 10.9 or 12.9. The first number is the nominal tensile strength in hundreds of MPa and the two together give the yield as a fraction of it, so 8.8 is 800 MPa tensile and 640 MPa yield.

Can I use this chart for head bolts, wheel nuts or flange bolts?

No. Head bolts and many driveline fasteners are torque-to-yield or torque-angle, set by a seating torque plus an angle and replaced after use. Wheel nuts have a manufacturer's torque, pattern and re-torque interval. Flange and structural bolting follow their own procedures (ASME PCC-1 practices, CSA S16 and RCSC). In every case the manufacturer's or code's specification overrides a generic chart, which is for plain steel bolts in ordinary joints where no figure has been published.

11Practice for this exam

Bolt torque is one fastener fact among many on the 433A and 421A exams. TicketPrep practice tests for both trades follow the Red Seal Program's block-by-block breakdown, and every answer is explained, including why each wrong option is wrong. You can try free sample questions with no account.

Ten free questions per trade, no account: free practice questions. How our questions are written and checked: how our questions are made.

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