AN4 Bolts -- Undrilled Head
AN4 bolts have a 1/4-28 UNF thread with 0.469 inch thread length (except AN4-3A, which has 0.406 inch thread length).
A or no A? AN bolts were originally designed to be used with a castle nut and cotter pin, so the base part number indicates a drilled shank. The addition of an "A" at the end (for example, AN4-13A) indicates an undrilled head and an undrilled shank for use with a self-locking nut.
AN bolt nomenclature can be confusing. Please take a look at our page on Identifying AN Bolt Sizes.
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