A325 bolts and A490 bolts are specialized, heavy hex structural bolts designed to withstand the loads of steel-to-steel connections. The head of the heavy hex structural bolt is specified to be the same size as the heavy hex nut of the name nominal diameter, allowing a single size wrench or socket to be used on the bolt head and nut. The structural bolt is designed with a shorter shank/thread length than the standard hex bolt or hex cap screw since these bolts are used for steel-to-steel connections.
ASTM A325 Bolts
ASTM A325 structural bolts are heavy hex bolts made of medium carbon steel with a flat bearing surface, washer faced, and chamfered point. They are commonly used in structural steel joints in heavy construction and available in diameters ranging from 1/2” up to 1-1/2”. A325 bolts come in two types.
Type 1 is a medium carbon steel and can be galvanized; Type 3 is a weathering steel that offers additional corrosion resistance. These Type 3 A325 bolts shall be marked “A325” to set them apart from standard A325 bolts.
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ASTM A490 Bolts
ASTM A490 bolts are heavy hex bolts made of alloy steel with a flat bearing surface, washer faced, and chamfered point. They are used in structural steel joints in heavy construction applications that require greater yield and tensile strengths than those of an A325 bolt are required.
A490 bolts are available in diameters ranging from ½” up to 1-1/2” and come in two types. Type 1 bolts are made from alloy steel, and Type 3 is made from a weathering steel, which is approximately twice as resistant to corrosion as Type 1. These Type 3 A490 bolts shall be marked “A490” to set them apart from standard A490 bolts.
ASTM A490 bolts should not be galvanized or electroplated because the molten bath of zinc exceeds the bolt’s tempering temperature and would cause the bolt to anneal in the bath. The only coating allowed by the ASTM A490 standard is the ASTM F1136 Grade 3.
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