Trailer Coupler Lock, Designed To Fit 1-7/8", (48mm), 2" (51mm) & Most 2-5/16" (59mm) Trailer Couplers, Advanced Locking Mechanism Provides Resistance To Picking & Prying, Keyed To 0313, Uses Master Lock Key Blank K1BOX Or Ilco Blank M1 TV #320-952.