A tubing severing tool designed especially for adjusting the length of a thin walled tubular sleeve. The severing tool includes an internal support mandrel for internally supporting the sleeve on one side of the plane along which it is to be severed which has a recess at the projecting end, and a piercing member externally engaging the sleeve on the same side of the severance plane as the internal support mandrel and overlying the recess so that the piercing member pierces the sleeve at the severance plane as the mandrel and piercing member are forced toward each other. The mandrel and piercing member may be mounted in plier-type carriers to pivot the mandrel and piercing member with respect to each other. A holding tool may be provided to support the sleeve along the severance plane.