Square Head Bolt A4-70 | Anti-Rotation Machine Bolt Marine

Thesquare head bolt is a threaded fastener distinguished by its four-sided head that provides an anti-rotation bolt function — the square head can be gripped securely with an open-end wrench or embedded against a flat surface to prevent the bolt from turning during tightening. This makes the square head machine bolt particularly valuable in confined spaces where holding a wrench on both ends is impractical, such as blind-side installations on equipment frames and machinery baseplates.

In marine and offshore environments, square head boltsinA4-70andA2-70 stainless steel are used to secure engine-driven pumps, generators, compressors, and deck machinery to their foundation plates. The anti-rotation square head eliminates the need for a backing wrench in tight machine compartments, while the stainless steel construction delivers saltwater corrosion resistance essential for shipboard service. Common applications include winch base mounting on workboat decks, hydraulic power unit anchoring, and equipment rail fastening where vibration loosening is a concern.

Oursquare head bolts are manufactured from austenitic stainless steel in grades A2-70 (304) for general marine use and A4-70 (316) for enhanced chloride resistance in splash zones. Available in metric sizes M4 through M18 with standard metric coarse threads, each bolt is passivated after machining to restore the protective chromium oxide layer. Custom lengths, full-thread and partial-thread configurations, and matched square nuts are available on request to support marine equipment boltassemblies.

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