An Expanding Spline Mandrel is a precision workholding tool designed to grip a component using its internal spline by expanding inside it. It provides secure, concentric holding for machining, inspection, or balancing without damaging the spline profile.

Expanding mandrels on a lathe are a type of mandrel that grip the interior diameter or ID of a workpiece. On an expanding mandrel, the shaft and sleeve have corresponding tapers and are machined from hardened steel. The sleeve is slotted and expands when pressed into the tapered shaft.