Machine Bolts

Machine bolts are heavy, coarse-threaded bolts with a square or hex head, used in machinery, structural timber, and heavy assembly. Larger and more robust than standard hex bolts in their traditional form, they're specified for utility, agricultural, and construction applications and for restoration of older equipment. We stock machine bolts in steel across common grades.

What Machine Bolts Are

Machine bolts are externally threaded fasteners with a large square or hex head, mated with a nut, traditionally used where heavy, coarse-thread fastening is needed — pole-line hardware, timber framing, machinery bases, and utility construction. They're typically furnished in lower-to-medium strength grades suited to general heavy-duty use rather than high-tension structural joints.

Square vs. Hex Head

Square head: the traditional machine bolt head, offering strong wrench grip and a period-correct look for restoration and utility work. Hex head: the modern standard, easier to wrench in tight spaces. Choose by equipment specification and wrench access.

Grades and Finishes

Grade 2 low-carbon steel for general use and Grade 5 for higher strength, typically plain or zinc plated, with hot-dip galvanized for outdoor utility and timber work. Match grade to the load and finish to the environment.

Selecting the Right Machine Bolt

Match the head style to the equipment or spec, the grade to the load, and the length to the assembly plus nut. Choose galvanized for exterior timber and utility use. Pair with a matching nut and washer, and verify coarse thread pitch. For high-strength structural joints, use a graded structural bolt instead.

Use the filters to narrow by size, length, head style, and grade. Orders before 12 PM ET ship same day.