Hex bolts, Zinc plated grade 8 steel yellow

Hex bolt diameter is measured on the outside of the threads.

Hex bolt diameter

Resources

Diameter and Thread count
Coarse (standard) thread 1/4"-20 5/16"-18 3/8"-16 7/16"-14 1/2"-13 9/16"-12 5/8"-11 3/4"-10 7/8"-9 1"-8 1-1/8"-7 1-1/4"-7 Fine thread 1/4"-28 5/16"-24 3/8"-24 7/16"-20 1/2"-20 9/16"-18 5/8"-18 3/4"-16 7/8"-14 1"-14 ^

^ NOTE: While 12tpi is the fine thread (UNF) standard, 14tpi is far more common in actual use.