Abstract: There is disclosed coin billet or coining die holder (108) for a robotic arm of a polishing machine for polishing a coining die or coin billet. The holder comprises a base (114); a magnetic retainer (122) which is arranged to magnetically retain a billet or die to the base; and a supporting sidewall (128)extending away from the base in an axial direction. The supporting sidewall is arranged to at least partially surround the outer surface of a billet or die retained to the base by the magnetic retainer so as to restrict lateral movement of the billet or die with respect to the base.