Abstract: A device for use in piercing and plugging mills, comprising a rod with a plug and a gear, for keeping the rod from longitudinal displacements under the effect of the load arising during the piercing or plugging. The gear includes a fixed thrust bearing accommodating a revolving casing through which passes the rod that reciprocates in operation. A part of the internal surface of the revolving casing forms a working cone that faces the plug with its base. The gear also includes a lock to fix the rod when piercing or plugging a billet, and preferably mounted on the rod, and a drive for carrying the rod with the plug. The lock mounts a spring-biased cone positively encompassed round the circumference with radially floating cams. Before piercing, the spring-biased cone is slightly drawn off by the spring from the cams so that the latter can enter the lock which is then able to enter the casing.