Called a locking tonque buckle, the eye is for a padlock.
Ha Ha Ha, so I looked up what you said.
Found this first. (Buckles for your BDSM projects
Buckles come in many different styles, but they are all meant for the same purpose; to hold two straps together. We have put together the best selection of BDSM buckles available anywhere. Our selection of buckles includes locking buckles, center bar buckles with and without rollers, heel bar buckles and conway buckles; the right buckles for your projects.
Locking Buckles
The locking buckles below, in both standard and center bar styles, are very popular among BDSMers. The tongue has a loop at its end, large enough to take a small lock such as those in the padlock section. The closure cannot be opened with a lock in place. Great for bondage gear. Gear made with these buckles should use 1/2" oblong slots in the tongue strap. We offer the oblong punches in our tool section. All of these locking roller buckles are zinc die castings.
locking center bar roller buckle
Center Bar Locking Roller Buckles
Heavy duty, single tongue with lock loop. These buckles have a heel bar that functions as a strap keeper.)
So I'm like what is BDSM? So I looked it up and got this.
(Bondage and discipline consist of using physical or psychological restraints, domination and submission involve an exchange of power and control, and sadism and masochism refer to taking pleasure in others' or one's own pain or humiliation.)
That would explain the Pink Leather Belt that dissolved when I dug it up.
