Definition of T bolt. 1 : a bolt having a crosspiece for a head. 2 : a bolt with a head of square or rectangular shape intended to fit a T slot.
A bolt with a T-shaped head, made to fit into a T-shaped slot in a drill swivel head; by means of it the swivel head can be turned to any angle of inclination to drill a borehole. Also, a similar bolt made to fit into a T-slot in the bed of a machine, for the purpose of holding a piece of metal to be machined or to fasten a machine to its base.