A coupler includes one or more pairs of ears each having an orifice, a lever having one end engaged between the ears and having an aperture aligned with the orifices of the ears for receiving a locking pin. The locking pin includes a head formed on one end and having an inner flat peripheral surface for solidly engaging with the ears, and includes an opening formed in a peripheral wall which may be expanded radially outward to engage with the ears, for solidly securing the locking pin to the ears. A retaining ring may solidly secure the locking pin to the ears.