Head Marking | SLS Bolts & Nuts

Head Marking

It is important to recognize the head mark on every fasteners so as to ascertain the correct grade of fasteners to be
used. The following are the standard head markings for both metric and imperial fasteners

	Metric Steel Bolts
Standards	ISO 898 Part 1
Identification Mark
Product Specifications	Grade 4.8	Grade 5.8	Grade 8.8 <= M16 (> M16)	Grade 10.9	Grade 12.9 Socket Head Cap Screws
Material	Low/Medium Carbon Steel	Low/Medium Carbon Steel	Medium Carbon Steel Heat Treated	Alloy Steel Heat Treated	Alloy Steel Heat Treated
Min. Tensile Strength (MPa)	420	520	800 (830)	1040	1220
Min. Yield Strength (MPa)	340	420	640 (660)	940	1100
Proof Load (MPa)	310	380	580 (600)	830	970
Hardness (Min-Max)	HV130-220	HV 160-220	HRC 22-32 (HRC 23-34)	HRC 32-39	HRC 39-44
Compatible Nut	Class 4	Class 5	Class 8	Class 10	-

	Metric Steel Bolts
Standards	BS 4190
Product Specifications	Grade 4.6	Grade 4.8	Grade 6.8	Grade 8.8	Grade 10.9
Material	Low/Medium Carbon Steel	Low/Medium Carbon Steel	Low/Medium Carbon Steel Heat Treated	Medium Carbon Steel Heat Treated	Alloy Steel Heat Treated
Min. Tensile Strength (N/mm²)	400	400	600	800	1000
Min. Yield Strength (N/mm²)	240	320	480	640	900
Hardness (Min-Max)	HV 120-220	HV 160-220	HV 190-250	HRC 22-32	HRC 32-39
Compatible Nut	Class 4	Class 4	Class 6	Class 8	Class 10

Note : When a thick protective coating is applied to a bolt of grade 8.8 or 10.9, which requires the nut thread to be overtapped, the next higher grade of nut should be used.

	Inch Steel Bolts
Standards	SAE J429
Identification Mark
Product Specifications	Grade 2	Grade 5	Grade 8
Nominal Size Range	1/4 - 3/4 (>3/4 - 1-½)	1/4 - 1 (>1 - 1-½)	1/4 - 1-½
Material	Low/Medium Carbon Steel	Medium Carbon Steel Heat Treated	Medium Carbon Steel Heat Treated
Min. Tensile Strength (psi)	74000 (60000)	120000 (105000)	150000
Min. Yield Strength (psi)	57000 (36000)	92000 (81000)	130000
Proof Load (psi)	55000 (33000)	85000 (74000)	120000
Core Hardness (Min-Max)	HRB 80-100 (HRB 70-100)	HRC 25-34 (HRC 19-30)	HRC 33-39
Compatible Nut	Grade 2	Grade 5	Grade 8

For detailed information, please refer to complete governing standards.