The HitchMate Trailer Hitch Lock is great for securing your bike rack or trailer to the hitch. It has a 0.625" diameter and fits 2" x 2" trailer hitches (Class III and Class IV). It's inside width is 2.625" and has an overall length of 6". The weather-resistant lock features a covered key opening for added durability. It also comes with two keys for your safety and convenience.