Mechanical Properties of Steel Bolts and Screws (Excerpt from JIS B 1051-2000)

2026/05/07

Mechanical Properties by Strength Grade

Mechanical Properties				Strength Classifications
				3.6	4.6	4.8	5.6	5.8	6.8	8.8		9.8 × 2	10.9	12.9
				3.6	4.6	4.8	5.6	5.8	6.8	Nominal d ≤ 16*1	d > 16*1	9.8 × 2	10.9	12.9
Tensile strength Rm 3 4 [N/mm²]		Nominal		300	400		500		600	800	800	900	1,000	1,200
Tensile strength Rm 3 4 [N/mm²]		Minimum		330	400	420	500	520	600	800	830	900	1,040	1,220
Hardness	Vickers hardness HV	Minimum		95	120	130	155	160	190	250	255	290	320	385
	Vickers hardness HV	Max		220*5					250	320	335	360	380	435
	Brinell hardness HB	Minimum		90	114	124	147	152	181	238	242	276	304	366
	Brinell hardness HB	Max		209*5					238	304	318	342	361	414
	Rockwell hardness	HRB	Minimum	52	67	71	79	82	89	-	-	-	-	-
		HRB	Max	95.0*5					99.5	-	-	-	-	-
		HRC	Minimum	-	-	-	-	-	-	22	23	28	32	39
		HRC	Max	-						32	34	37	39	44
Surface hardness: HV0.3		Maximum		-						*6
Yield strength: ReL *7 [N/mm²]		Nominal		180	240	320	300	400	480	-
Yield strength: ReL *7 [N/mm²]		Minimum		190	240	340	300	420	480	-
0.2% proof stress: Rp0.2 * 8 [N/mm²]		Nominal		-						640	640	720	900	1,080
0.2% proof stress: Rp0.2 * 8 [N/mm²]		Minimum		-						640	660	720	940	1,100
Guaranteed load stress		Stress ratio		0.94	0.94	0.91	0.93	0.90	0.92	0.91	0.91	0.90	0.88	0.88
Guaranteed load stress		[N/mm²]		180	225	310	280	380	440	580	600	650	830	970
Elongation at break δ [%]		Minimum		25	22	-	20	-	-	12	12	10	9	8
Wedge tensile strength				Must not be less than the minimum tensile strength
Impact strength [J]		Minimum		-			25	-	-	30	30	25	20	15
Head Impact Strength				Must not be damaged
Height of the non-decarburized portion of the thread山　E		Minimum		-						1/2H1			2/3H1	3/4H1
Depth of fully decarburized section G [mm]		Maximum		-						0.015

For structural steel bolts with a strength class of 8.8, the classification is based on a nominal thread diameter of 12 mm.
Strength Class 9.8 applies only to screws with a nominal diameter of 16 mm or less.
The minimum tensile strength applies to products with a nominal length of 2.5d or more; for products with a nominal length of less than 2.5d or those that cannot be subjected to a tensile test (e.g., those with special head shapes), the minimum hardness applies.
For tensile tests conducted on the product in its as-is condition, use a value calculated based on the minimum tensile strength Rm,min.
The hardness of the threaded ends of bolts, screws, and anchor bolts shall not exceed 250 HV, 238 HB, or 99.5 HRB.
For products in strength classes 8.8 to 12.9, the difference between the surface hardness and the internal hardness, measured using the Vickers hardness scale (HV0.3), must not exceed 30 points. However, for products in strength class 10.9, the surface hardness must not exceed 390 HV.
For materials for which the yield point ReL cannot be measured, use the 0.2% proof stress Rp0.2. The ReL values for strength classes 4.8, 5.8, and 6.8 are intended for calculation purposes only and are not test values.
The yield stress ratio and minimum 0.2% proof stress (Rp0.2), as specified in the strength classification guidelines, apply to tests conducted on machined test specimens. If these values are determined through testing of the actual product, they may vary due to factors such as the manufacturing method or the nominal diameter of the screw.

The values of H1 and (E min)

Unit [mm]

Screw pitch P			0.5	0.6	0.7	0.8	1	1.25	1.5	1.75	2	2.5	3	3.5	4
H1			0.307	0.368	0.429	0.491	0.613	0.767	0.920	1.074	1.227	1.534	1.840	2.147	2.454
E (Minimum)	Strength Class	8.8, 9.8	0.154	0.184	0.215	0.245	0.307	0.384	0.460	0.537	0.614	0.767	0.920	1.074	1.227
		10.9	0.205	0.245	0.286	0.327	0.409	0.511	0.613	0.716	0.818	1.023	1.227	1.431	1.636
		12.9	0.230	0.276	0.322	0.368	0.460	0.575	0.690	0.806	0.920	1.151	1.380	1.610	1.841

Mechanical Properties and Maximum Tightening Torque of Hex Socket Head Cap Screws (for Class 10.9 and 12.9 Fine Thread Screws)

For reference

Nominal d	Effective cross-sectional area [mm^²]	Minimum tensile load [N]		Yield load [N]		Guaranteed load [N]		Maximum allowable axial force F [N]		(Tf max.) Maximum tightening torque [N·m]
		Minimum tensile load [N]		Yield load [N]		Guaranteed load [N]		Maximum allowable axial force F [N]		When K = 0.17		When K = 0.25
		10.9	12.9	10.9	12.9	10.9	12.9	10.9	12.9	10.9	12.9	10.9	12.9
M1.6	1.27	1,320	1,550	1,190	1,390	1,050	1,230	832	976	0.23	0.27	0.33	0.39
M2	2.07	2,150	2,530	1,940	2,270	1,720	2,010	1,360	1,590	0.46	0.54	0.68	0.80
M2.5	3.39	3,530	4,140	3,170	3,720	2,810	3,290	2,220	2,610	0.94	1.11	1.39	1.63
M3	5.03	5,230	6,140	4,710	5,520	4,180	4,880	3,300	3,870	1.68	1.97	2.47	2.90
M4	8.78	9,130	10,700	8,220	9,640	7,290	8,520	5,750	6,750	3.91	4.59	5.75	6.75
M5	14.2	14,800	17,300	13,300	15,600	11,800	13,800	9,300	10,900	7.91	9.28	11.6	13.6
M6	20.1	20,900	24,500	18,800	22,100	16,700	19,500	13,200	15,400	13.4	15.8	19.8	23.2
M8	36.6	38,100	44,600	34,300	40,200	30,400	35,500	24,000	28,100	32.6	38.3	48	56.3
M10	58.0	60,300	70,800	54,300	63,700	48,100	56,300	38,000	44,600	64.6	75.8	95	111
M12	84.3	87,700	103,000	78,900	92,600	70,000	81,800	55,200	64,800	113	132	166	194
M14	115	120,000	140,000	108,000	126,000	95,500	112,000	75,300	88,400	179	210	264	309
M16	157	163,000	192,000	147,000	172,000	130,000	152,000	103,000	121,000	280	328	411	483
M18	192	200,000	234,000	180,000	211,000	159,000	186,000	126,000	148,000	385	452	566	664
M20	245	255,000	299,000	229,000	269,000	203,000	238,000	161,000	188,000	546	640	803	942
M22	303	315,000	370,000	284,000	333,000	252,000	294,000	199,000	233,000	742	871	1,090	1,280
M24	353	367,000	431,000	330,000	388,000	293,000	342,000	231,000	271,000	944	1,110	1,390	1,630
M27	459	477,000	560,000	430,000	504,000	381,000	445,000	301,000	353,000	1,380	1,620	2,030	2,380
M30	561	583,000	684,000	525,000	616,000	466,000	544,000	368,000	431,000	1,870	2,200	2,760	3,230

K: Torque coefficient

Notes

The minimum tensile load and guaranteed load in the table above are based on JIS B 1051:2000.
Yield load = Ultimate strength (lower yield point) × Effective cross-sectional area
The maximum allowable axial force is approximately 0.7 times the yield load, and the maximum tightening torque (Tfmax) is calculated as the torque coefficient (K) multiplied by the maximum allowable axial force (F) and the nominal diameter (d).
Value of torque coefficient K = 0.17: Oil lubrication, fastened material SS400, fastened surface finish approximately 25S, female thread material SS400, female thread accuracy 6g or Grade 2
For a value of K = 0.25: electrogalvanized coating, fastened material SS400, fastened surface finish approximately 25S, female thread material SCM, female thread accuracy 6g or Grade 2
Note: If the material of the female thread mentioned above is SS400, the value of K is 0.35.

Recommended tightening torque (Tf)

The recommended tightening torque (Tf) varies depending on the tool used, as there can be variations in the initial tightening force.
Recommended tightening torque (Tf) = Tool-specific value × Maximum tightening torque (Tfmax)
- Figures by Tool Type
- 1) When tightening by hand: 0.65 Tfmax.
- 2) When using an impact driver or power driver: 0.75 Tfmax.
- 3) When using a torque wrench or a wrench with torque limiting function: 0.85 Tfmax.
- 4) For torque wrenches: 0.9 Tfmax.

Note: The values above are for reference only. When using these products, please determine the proper tightening torque in accordance with JIS B 1083, 1084, and other relevant standards.

Mechanical Properties of Steel Bolts and Screws (Excerpt from JIS B 1051-2000)

Mechanical Properties by Strength Grade

The values of H1 and (E min)

Mechanical Properties and Maximum Tightening Torque of Hex Socket Head Cap Screws (for Class 10.9 and 12.9 Fine Thread Screws)

Recommended tightening torque (Tf)

Other Technical Documents

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Hole Machining, Tolerances, and Fits

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