What does 307A mean on a bolt?
Commercial-grade 8 bolts are the strongest option available. They’re made from medium carbon alloy steel and have markings that include six raised dashes. The psi of the bolt is 150,000, meaning that it can withstand great deals of pressure because of the way it was quenched and tempered.
Grade B7 is a heat-treated chromium-molybdenum alloy steel with minimum tensile requirement of 100 ksi, yield of 75 ksi and maximum hardness of 35 HRC. ASTM A193 specification covers requirements for chemical composition, mechanical properties, hardness, heat-treatment, recommended nuts-washers for Grade B7 fasteners.
Grade C. Grade C is a thru-hardened medium carbon zinc plated alloy steel. No head markings (manufacturers mark may also be included). Finish is equivalent in strength to Grade 8 but without the yellow color.
ASTM A307 bolts are not assigned to a group since they are not considered to be high strength bolts. The ultimate tensile strengths for A325 and A490 bolts are 120 ksi and 150 ksi respectively.
What do the letters on bolts mean?
307A bolts are a Grade 1 equivalent that is used in low-strength application. It has lower hardness and tensile requirement than grade 2 bolts. It is generally used in low-pressure, standard or normal temperature applications and is made of low carbon steel.