Square Head Bolts

Square head bolts have a four-sided head that provides excellent wrench grip and a traditional industrial appearance. Once the dominant bolt head before hex became standard, they remain specified for machinery, set screws, agricultural equipment, and restoration work. We stock square head bolts and set screws in steel and stainless.

Why Square Heads

The four flats give a wrench solid purchase and were easy to forge, which is why square heads dominated early machinery. Today they're chosen for heavy-equipment durability, period-correct restoration, and square head set screws where the projecting head allows hand or wrench adjustment on collars and shafts.

Square Head Set Screws

Square head set screws have a projecting square head (unlike headless socket set screws), used to lock collars, gears, and pulleys where the head can be wrenched and provides positive grip. They're common on older machinery and where high holding torque is applied by wrench.

Materials and Finishes

Steel with zinc plating or plain finish for general and machinery use. 18-8 stainless for corrosion resistance. Choose by environment and the equipment's original specification.

Dimensional Standards

Square head bolts and set screws follow ASME B18.2.1 (bolts) and ASME B18.6.2 (square head set screws).

Selecting the Right Square Head Bolt

Match to the equipment's original specification for restoration, or choose for heavy-duty wrench grip. Select material for the environment, and verify thread pitch. For square head set screws, ensure the projecting head clears surrounding parts through its full rotation.

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