B&B’s Thread Cleaning Tap Set will restore and clean bolt holes in blocks, heads and other threaded parts without under cutting the original threads. This allows for proper torque when re-using parts. The set is made from 4130 chrome moly steel and is heat treated for maximum hardness. Set includes 1/4”, 5/16”, 3/8”, 7/16”, 1/2”, and 9/16” NC./NF.