ARP's handy thread cleaning chaser taps are designed with correct thread pitch and diameter to clean dirty blind or thru holes. Taps come in five USS sizes: 1/4", 5/16", 3/8", 7/16" and 1/2", as well as metric. They are sold individually or in sets. Please note that these are strictly cleaning taps and are not designed to cut thread. They are a handy addition to the tool box of any serious engine builder and an essential aid to preparing any block for final assembly. Don't take a chance on weakening block and cylinder head threads. Use these handy thread cleaning chasers whenever possible!