AN6H bolts have a drilled head for safety wire and 3/8-24 UNF threads. All AN6H bolts have a 0.641 inch thread length regardless of grip length. This thread length is designed to accommodate a full-height nut and one AN960-616 flat washer. Sold individually; nuts and washers sold separately. Grip Length refers to the length of the unthreaded portion of the shank. Grip lengths are available in 1/8" increments to match the thickness of the materials being bolted together (the threaded portion should never be positioned inside the hole). If your assembly is between sizes, select the next longer bolt and use additional AN960-616 and AN960-616L washers to take up the slack. 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, AN6H-20A) indicates an undrilled shank for use with a self-locking nut. UHL: Under Head Length (also known as Full Shank Length or Overall Length not including bolt head) AN bolt nomenclature can be confusing. Please take a look at our page on Identifying AN Bolt Sizes.