AN4 bolts have a 1/4-28 UNF thread. All sizes of AN4 bolts have a 0.469 inch thread length (except AN4-3A, which has 0.406 inch thread length). The thread length is designed specifically to fit a full-height nut plus one AN960-416 washer.
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 AN960-416 and AN960-416L washers to take up the slack.