These roller buckles are designed to accept a small padlock through the tongue of the buckle, thereby making it impossible to remove whatever strap it is on. However, it is not necessary to use a lock if it is not wanted at that point, as the tongue functions as a regular tongue as well. These have many different uses, and are perfect when a moderate degree of security is desired (naturally, the thief could always cut the leather). It will, however, prevent casual tampering, and will certainly deter pickpockets. To utilize this buckle you will need a oval punch (specifically, a 3/8 inch oval punch) to make the proper size holes in the strap. Here's some additional information:
What's all this about heel bar buckles, center bar buckles, cart buckles and such? | 
