5/16" Shank, 14-40TPI .300 Cutting Diameter, 1" Reach, .002 Crest/Flat, .218 Neck, 3" overall, Single Form Thread Mill. Solid Carbide. Made in USA Please Note: These are not 3/8" cutting diameter Endmills. The 3/8" means you can thread mill an internal thread as small as 3/8"-16.