Fastener Tightening Torque Information

Adjustment of Torque for Tightening method and Friction Coefficient

Two major points have to be accounted for when installing a fastener.

1. Inaccuracy of torque wrench tightening method can range anywhere from ±17 to ±23%
2. The friction coefficient changes when using lubrication on the thread.

1. Inaccuracy of tightening method

A torque wrench has a “scatter” (tolerance) of ±17% to ±23%. We must account for this in order not to over-tighten the fastener.

Example:

A M30-12.9 fastener has a maximum tightening torque of 2,280 Nm, based on a friction coefficient of 0.125 (zinc plated)
Maximum torque: 2,280Nm (= 123%) (or 117%)
Mean torque if scatter is +23% = 2,280 / 1.23 = 1,854 Nm
Minimum torque if scatter is +23% = 1,854 x 0.77 = 1,428 Nm

Torque should be set to 1,854 Nm (mean torque) on the torque wrench

The accuracy of the tightening method needs to be accounted for, in order to not over-tighten the fastener.

2. Friction coefficient

The surface condition of a fastener may change the torque that can be applied and needs to be accounted for.

Friction coefficients for standard finish fasteners
Surface Condition		Lubrication Condition
Screw	Nut	Oiled	MoS2-Paste
- no treatment - phosphate	- no treatment	0.12-0.18	0.05-0.10
- electroplated appx. 8 μm	- electroplated appx. 5 μm	0.12-0.18
- dacromet-coated 6-8 μm	- dacromet-coated 6-8 μm	0.10-0.14

Example:

A M30-12.9 fastener using MoS2 paste.

A M30-12.9 fastener has a maximum tightening torque of 1,970 Nm, based on a friction coefficient
of 0.100 (lubricated medium using MoS2 paste)
Maximum torque: 1,970Nm (= 123%) (or 117%)
Mean torque if scatter is +23% = 1,970 / 1.23 = 1,602 Nm
Minimum torque if scatter is +23% = 1,602 x 0.77 = 1,234 Nm

Torque should be set to 1,602 Nm (mean torque)on the torque wrench

The accuracy of the tightening method, as well as the change in friction, needs to be accounted for in order not to over-tighten the fastener.

General Torque Figures

A torque value will be influenced by the fastening methods and tools used. The only way to determine an exact torque value is by actual application. The following figures are general guidelines only.

Figures in ft. lbs.

Thread Diameter	Property Class
Thread Diameter	8.8	10.9	12.9
M3	0.80	1.1	1.3
M4	1.8	2.6	3.1
M5	3.6	5.1	6.2
M6	7	10	12
M8	17	25	29
M10	33	48	58
M12	60	85	102
M14	97	137	165
M16	150	208	250
M18	201	287	342
M20	282	398	479
M22	390	552	664
M24	499	750	843
M27	746	1051	1266
M30	982	1383	1657
M33	1331	1875	2250
M36	1717	2407	2895
M39	2220	3120	3750
M42	2737	3840	4638
M45	3390	4762	5722
M48	4095	5775	6825
M52	5250	7387	9000
M56	6547	9225	11280
M60	8175	11475	13800
M64	9900	13950	17175
M68	12000	16950	20100
M72	14250	20100	24000
M76	16800	23625	28350
M80	19725	27600	33375
M85	24000	33225	40125
M90	28350	38925	47700
M95	33450	46875	56250
M100	39000	54750	66000

Torque - Metric Fasteners

Thread Diameter	Recommended Seating Torque (NM)												Proof Torque min. (NM)
	ISO 4762 DIN 912		DIN 7984	ISO 10642 DIN 7991		ISO 7380		ISO 7379	ISO 4014/ 4017 DIN 931 / DIN 933		ISO 4162		ISO 4026 / 4027 4028 / 4029
	Socket Cap Screws		Low Head Socket Cap Screws	Flat Head Countersunk Socket Cap Screws		Button Head Socket Cap Screws		Socket Shoulder Screws	Hexagon Head Cap Screws		Hexagon Flange Screws		Socket Set Screws
	10.9	12.9	10.9	10.9	12.9	10.9	12.9	12.9	10.9	12.9	10.9	12.9	45H
M1.6	0.25	0.30
M2	0.50	0.63
M2.5	1.03	1.27
M3	1.83	2.20	1.15	1.15	1.35	1.15	1.35						0.90
M4	4.27	4.83	2.70	2.70	3.10	2.70	3.10						2.50
M5	8.64	10.0	5.40	5.40	6.10	5.40	6.10		8.64	10.0	8.64	10.0	5.00
M6	14.7	16.8	9.15	9.15	10.5	9.15	10.5	5.6	14.7	16.8	14.7	16.8	8.50
M6.5								5.6
M8	35.6	41.0	22.0	22.0	26.0	22.0	26.0	9.6	35.6	41.0	35.6	41.0	20.0
M10	70.6	81.0	44.0	44.0	52.0	44.0	52.0	25	70.6	81.0	70.6	81.0	40.0
M12	123	142	77.0	77.0	90.0	77.0	90.0	51	123	142	123	142	65.0
M13								51
M14	195	226	122	122	143				195	226	195	226	65.0
M16	305	350	190	190	225	190	225	92	305	350	305	350	160
M18	420	485	262						420	485			310
M20	596	685	371	370	440			245	596	685			310
M22	811	930							811	930
M24	1031	1180							1031	1180
M25								485
M27	1508	1730							1508	1730
M30	2048	2380							2048	2380
M33	2787	3262
M36	3580	4190
M39	4633	5420

Torque - Imperial Fasteners

Thread Diameter	Recommended Seating Torque (in-lb)							Proof Torque min. (in-lb)
	ASME B18.3					ASME B18.2.1	IFI-111	ASME B18.3
	Socket Cap Screws	Low Head Socket Cap Screws	Flat Head Countersunk Socket Cap Screws	Button Head Socket Cap Screws	Socket Shoulder Screws	Hexagon Head Cap Screws SAE J429 Grade 8	Hexagon Flange Screws SAE J429 Grade 8	Socket Set Screws
#0	2.26		1.42	1.42				1.1
#1	4.01		2.52	2.52				2.1
#2	6.65		4.18	4.18				2.1
#3	10.1		6.33	6.33				6.0
#4	14.1	8.88	8.88	8.88				6.0
#5	20.8	13.1	13.1	13.1				11
#6	26.2	16.5	16.5	16.5				11
#8	48.0	30.1	30.1	30.1				23
#10	69.5	43.7	43.7	43.7				40
1/4	166	104	104	104	35	134	134	94
5/16	342	215	215	215	90	277	277	183
3/8	608	382	382	382	200	491	491	317
7/16	973	611	611			785	785	502
1/2	1484	931	931	931	363	1202	1202	750
9/16						1732	1732
5/8	2792	1722	1722	1722	922	2386	2386	1460
3/4	4952		3054		1864	4225	4225	2520
7/8	7991		4928			6823		5750
1	11979		7388		3443	10226		8000
1-1/8	16968		10464			14485
1-1/4	23944		14766		5637	20442
1-3/8	31394		19360			26806
1-1/2	41611		25692		12002	35573

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