Crankshafts

Crankshafts are obstacles first seen in Checkpoint 7 stage 2. They have a crank-like shaft of glass, and 3 Metals. The obstacle is joined to two metal pieces, that help it spin.

They are re-used in stage 2 (and it's variants) of 1st endless mode, as well as Local Multiplayer. They first appeared In the Smash Hit Gameplay Trailer of a (fake) Checkpoint 4, but that was NEVER used.

The crankshafts even have their own trailer (video link here, orhere).