Ball bearing

Ball bearings are a type of rolling-element bearing which use balls to maintain the separation between the moving parts of the bearing.

The Fourth Doctor "mocked" K-9 Mark I by handing him a bag of sweets and asking if he would like a ball bearing.(DW: The Invasion of Time)

The Tenth Doctor thought the commonly seen Earth cupcakes with edible ball bearings were "genius", and said "no other species in the galaxy has ever bothered to make [them]". (DW: Fear Her)