Leg Vice
From DT Online
The Blacksmiths' Leg Vice (aka Post Vice) firmly holds hot iron while it is hammered, chiseled or twisted. A normal Engineers Vice would soon shatter after such treatment because of the brittle nature of Cast iron from which they are made - Leg Vices were traditionally made from Wrought Iron and are still forged in steel.
The Leg ensures that the forces it is subjected to are transmitted through to the floor.