The RIDGID K9-204 4" CARBIDE (64318) FlexShaft 3-Chain Knocker with Carbide Tip is designed for use with the K9-204 FlexShaft Drain Cleaning Machine and provides wall-to-wall cleaning in 4 in. pipes. The chain knocker expands to a pipe's inside diameter to break up blockages. The model 64318 Chain Knocker fits 5/16 in. cable and is equipped with three chains. The carbide tipped chain knocker is ideal for cleaning hard-walled pipes, including for soft blockages, grease, scale, and roots.