Prior to its withdrawal in 2016, the ASTM A490 specification covered quenched and tempered, alloy steel, heavy hex structural bolts from 1/2″ diameter through 1-1/2″ diameter with a minimum 150 ksi tensile. These bolts are intended for use in structural connections and therefore have shorter thread lengths than standard hex bolts. Refer to the Structural Bolts page of our site for thread lengths and other related dimensions. A490 bolts are similar in application and dimensions to A325 heavy hex structural bolts but are made from alloy steel rather than medium carbon steel, resulting in a higher strength fastener. The A490 specification is applicable to heavy hex structural bolts only. For bolts with different thread lengths than specified for structural bolts but with similar mechanical properties, see Specification A354 grade BD. ASTM A490 bolts shall not be coated by hot-dip galvanizing, mechanical deposition, or electroplating with zinc due to the potential risk of hydrogen embrittlement. ASTM has approved coating A490 bolts with Zinc/Aluminum Corrosion Protective Coatings per ASTM F1136 Grade 3, commercially called Geomet. Additional testing in the form of Magnetic Particle Inspection for Longitudinal Discontinuities and Transverse Cracks is a requirement of the A490 specification.