A325 structural bolts are used in heavy-duty applications for fastening two pieces of structural steel together. A325 bolts are made only in steel and are solely used for making steel-to-steel connections; these bolts are inappropriate for connecting steel to concrete, wood or other structural materials.
The American Society for Testing and Materials International sets the diameter, length and load standards for A325 structural bolts. These bolts are manufactured in diameters between 0.5 and 1.5 inches. Manufacturers produce A325 bolts in a variety of lengths, but ASTM prohibits manufacturing A325 bolts in lengths greater than 5 inches. A325 bolts are exclusively hexagonal-headed steel structural bolts; similar bolts for other applications use ASTM's A490 standard.
A325 bolts are only available in short lengths due to their use in structural applications. A bolt's weakest point is its threaded length. Use of a longer bolt places more strain on its weaker threaded section, lowering the bolt's overall strength and increasing its chance of failure.
A325 structural bolts are available in two main types according to their constituent materials. Type 1 A325 bolts are made of various grades of carbon steel alloys. Weathering steel bolts are available under the Type 3 specification. ASTM withdrew the Type 2 specification for A325 bolts in 1991. Tempered or quenched steel bolts of similar size and function use the A490 standard.