Pair these S-code holders with a compatible carbide insert (sold separately) to cut threads inside a workpiece. Inserts sit lower in these holders than in other types of holders, which gives you extra clearance for threading close to a shoulder. Their clamp also holds the insert more securely, so you can create more precise threads. Fit these holders directly into a lathe tool post or holder—no tool block needed. They cut in a right-hand direction, meaning the holder moves from right to left toward the lathe chuck. They’re also known as indexable insert holders.