It's imperative to have clean and straight threads to achieve proper torque when rebuilding an engine. Our high-quality tap sets will restore and clean bolt holes in blocks, heads, components, etc., without undercutting. We offer sets in both N.C. and N.F. thread types, and all sizes are stamped for ease of identification. Both of our six piece sets are packed in a plastic pouch and include sizes 1/4", 5/16", 3/8", 7/16", 1/2", and 9/16".