The Collaborative International Dictionary
Expanding bit
Expanding \Ex*pand"ing\, a. That expands, or may be expanded; extending; spreading; enlarging.
Expanding bit, Expanding drill (Mech.), a bit or drill made adjustable for holes of various sizes; one which can be expanded in diameter while boring.
Expanding pulley (Mach.), a pulley so made, as in sections, that its diameter can be increased or diminished.