ASTM A490M heavy hex bolt specification covers two types of quenched and tempered. Alloy steel, heavy hex structural bolts having a tensile strength of 150 to 173 ksi.
A490 bolts are more good than A325 bolts which are 120/105 minimum tensile strength steel. To minimize the risk of brittle fracture A490 bolts have both a minimum and a maximum tensile strength specified. FHWA recommends that A325 bolts be used wherever possible.
ASTM A490 and ASTM A490M are standards for heavy hex structural bolts made from alloy steel. The imperial standard for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength, while the standard (M) is titled Standard Specification for High-Strength Steel Bolts, Classes 10.9 and 10.9.3, for Structural Steel Joints
A490 covers heavy hex structural bolts (tensile strength of 150 to 173 ksi) and currently, ASTM Standards do not allow hot-dip galvanizing of A490 bolts for corrosion protection. A490 only allows a type of zinc/aluminum coating to be used on high-strength bolts.
These bolts are equivalent to ASTM A325 bolts in application and geometry, but are made to a higher strength. The imperial grades are made to the same strength specifications as ASTM A354 grade BD. The metric grades are made to the same strength specifications as ASTM F568M property class 10.9. Also, unlike their weaker counterparts they may not be coated by hot-dip galvanization, mechanical deposition, or electroplating.
Because these bolts are designed to be used in structural applications the threaded length of the bolts are shorter to keep the threads out of the joint.