Metric Hex Head Bolt Markings

Most often bolts used in machinery are made to saestandard j429 and bolts used in structures are made to various astmstandards.

Metric hex head bolt markings.

Some bolts share identical head identification and have significantly different strengths. Jis b1180 and three sizes of iso 4014 and iso 4017 have heads that are smaller than their din. Common metric steel bolts identification mark 4 6 x 5 8 x 8 8 x 10 9 x or 12 9 1 2 9 m x product specification class 4 6 class 5 8 class 8 8 class 10 9 class 12 9 socket head cap screw material low medium carbon steel low medium carbon steel heat treated medium carbon steel heat treated alloy steel heat treated alloy steel heat treated. Hex head bolt markings the strength and type of steel used in a bolt is supposed to be indicated by a raised mark on the head of the bolt.

Head markings metric bolt class mechanical properties proof load mpa min yield mpa min tensile strength mpa class 8 8 medium carbon steel quenched and tempered 580 600 640 660 800 830 class 10 9 alloy steel quenched and tempered 830 940 1040 class 12 9 alloy steel quenched and tempered 970 1100 1220 a2 stainle. Determining bolt grades understanding head markings the nut and bolt solution series. Head marking class and material nominal size range mm mechanical properties. The type of mark depends on the standard to which the bolt was manufactured.

With an extended tip that locks into a mating hole or slot sometimes known as a dog point they are often used to align and secure parts such as gears and pulley wheels. Examples of markings on socket head cap screws. These numbers do not give us any insight as to the size or hardness of the bolt. We see bolts with a 9 or a 7 perhaps even a 10 stamped in the head.

Identification with the manufacturer s mark and the property class is mandatory for hexagon screws 3 6 to 12 9 and socket head cap screws 8 8 to 12 9 with thread diameter d 5mm where the shape of the screw always allows it preferably on the head. Examples of markings on hexagon screws. For partially threaded the minimum thread length is longer for larger bolt sizes. 16mm 72mm.

Hex bolt identification markings and strength chart table guide. Select from partially threaded or fully threaded. Yield strength mpa min. Turn these metric screws by hand using the hex head or tighten them with a wrench for extra torque.

Class 10 9 alloy steel quenched and tempered. 5mm 100mm. All sizes below 16mm. Tensile strength mpa class 8 8 medium carbon steel quenched and tempered.

All short lengths are fully threaded. Determining bolt grade and head markings. Metric grades 8 8 10 9 and 12 9 socket products. Metric head markings many metric automotive bolts are stamped with numbers creating a lot of confusion as to the actual grade hardness of the bolt.

Proof load mpa min. Additonal information on bolts is located at the bottom of the webpage.