The one with a lock is a -2 and the one without is a -1. Otherwise, they're exactly the same.
As in Model 642-1. Spoken, "Six forty-two dash one". Or it might be written M642-1.
Most of us prefer the -1 without the lock. But if you have little ones in the house, riding in your car, biting at your ankles, a locked gun might be nice to have.
BTW, these guns had a name in addition to the number. They are called.....
"Centennials"