The hammer is the bit holder and bit assembly, which includes the bit spacer. The hammer strikes against the anvil, breaking material up.

The bit holder can be referred to as the hammer without referring to the whole assembly.  A series of holders are welded to a shell rotor or secured in place by rotor pins to a pinned rotor in a predetermined pattern, each holding a grinding bit. Grinding bits are secured to the holders by bolts, washers, and lock nuts.