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Large Hexagon (National Standard)

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High-strength large hexagon bolts for steel structures

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Product Description

　　Application Fields
　　Friction-type connections for various steel structures, including long-span bridges, large steel roofs, power plant boiler steel structures, high-rise buildings, sports venues, tower and mast steel structures, and large port container cranes.
　　★ Product Series
　　△ China Standard GB/T 1228–1231: Heavy-Duty High-Strength Bolt, Nut, and Washer Assemblies for Steel Structures

Thread specification M		M12		M16		M20		M22		M24		M27		M30
P		1.75		2		2.5		2.5		3		3		3.5
dw	minute	19.2		24.9		31.4		33.3		38.0		42.8		46.5
k	Nominal	7.5		10		12.5		14		15		17		18.7
	maximum	7.95		10.75		13.40		14.90		15.90		17.90		19.75
	minute	7.05		9.25		11.60		13.10		14.10		16.10		17.65
k’	minute	4.9		6.5		8.1		9.2		9.9		11.3		12.4
r	minute	1.0		1.0		1.5		1.5		1.5		2.0		2.0
S	maximum	21		27		34		36		41		46		50
	minute	20.16		26.16		33		35		40		45		49
b	L	≤40	≥45	≤50	≥55	≤60	≥65	≤65	≥70	≤70	≥75	≤75	≥80	≤80	≥85
	nominal	25	30	30	35	35	40	40	45	45	50	50	55	55	60
L		25-75		45-130		50-160		55-220		60-250		65-280		70-320

Bolt/Nut/Washer Size Chart
Thread specification M			M12	M16	M20	M22	M24	M27	M30
Pitch P			1.75	2	2.5	2.5	3	3	3.5
Screw mother	dw	minute	19.2	24.9	31.4	33.3	38.0	42.8	46.5
	c	maximum	0.8	0.8	0.8	0.8	0.8	0.8	0.8
	c	minute	0.4	0.4	0.4	0.4	0.4	0.4	0.4
	m	maximum	12.3	17.1	20.7	23.6	24.2	27.6	30.7
	m	minute	11.87	16.4	19.4	22.3	22.9	26.3	29.1
	S	maximum	21	27	34	36	41	46	50
	S	minute	20.16	26.16	33	35	40	45	49
Pad circle	d2	minute	23.7	31.4	38.4	40.4	45.4	50.1	54.1
	d2	maximum	25	33	40	42	47	52	56
	d1	minute	13	17	21	23	25	28	31
	d1	maximum	13.43	17.43	21.52	23.52	25.52	28.52	31.62
	h	Nominal	3.0	4.0	4.0	5.0	5.0	5.0	5.0
		minute	2.5	3.5	3.5	4.5	4.5	4.5	4.5
		maximum	3.8	4.8	4.8	5.8	5.8	5.8	5.8
	d3	minute	15.23	19.23	24.32	26.32	28.32	32.84	35.84
	d3	maximum	16.03	20.03	25.12	27.12	29.12	33.64	36.64

Bolt, Nut, and Washer Compatibility Chart
Category	Bolt	nut	Washer
Model Dimensions	According to GB/T 1228	According to GB/T 1229	According to GB/T 1230
Performance Level	10.9S	10H	35–45 HRC
Performance Level	8.8S	8H	35–45 HRC

Bolt Materials and Mechanical Properties
Performance Level	Thread specification	Material	Tensile strength, MPa	Specified non-proportional extension MPa	Hardness HRC	Elongation (%)	Shrinkage rate %
10.9S	M12 to M24	20MnTiB	1040–1240	≥940	33–39	≥10	≥42
	M27–M30	35VB
8.8S	M12 to M24	20MnTiB	830–1030	≥660	24–31	≥12	≥45
	M27–M30	35VB

		Mechanical Properties of Nuts
Thread specification M		M12	M16	M20	M22	M24	M27	M30
Guaranteed Load (kN)	10H	87.7	163	255	315	367	477	583
Guaranteed Load (kN)	8H	70	130	203	251	293	381	466
Materials	10H	35 or 45 (GB/T 699), ML35 (GB/T 6478)
Materials	8H	35 or 45 (GB/T 699), ML35 (GB/T 6478)
Hardness	10H	Rockwell hardness: 98 HRB to 32 HRC; Vickers hardness: 222 to 304 HV30
Hardness	8H	Rockwell hardness: 95 HRB to 30 HRC; Vickers hardness: 206 to 289 HV30

Explanation Regarding the Torque Coefficient Test
High-strength large hexagon bolted connection assemblies are supplied with a guaranteed torque coefficient, with an average torque coefficient of 0.110 to 0.150 for bolts in the same batch and a torque coefficient deviation of less than 0.010. Each assembly consists of one bolt, one nut, and two washers, all manufactured in the same batch. The warranty period for the torque coefficient is six months from the date of manufacture.
Construction Code (in accordance with GB 50205-2001 Code for Acceptance of Construction Quality of Steel Structures)
1. Final tightening torque
Final tightening torque Tc = K · Pc · d
K—represents the torque coefficient, which can be obtained through three methods: 1) self-testing; 2) third-party testing; or 3) by referring to the quality assurance documentation we provide.
Pc —— is the prestressing force value; see Appendix Table B.0.3.
d —— the nominal diameter of the bolt. For example, the d value for an M24 bolt is 24.
2. Initial Tightening Torque
The initial tightening torque value, To, for high-strength large hexagon bolted connections shall be taken as 0.5Tc.