Metal buckles come as a wire loop, "standard" cut hinge, and pin hinge.
PIN HINGE
The older SP buckles had the "c" clips, but the clips were not of good corrosion resisting steel, but of a higher carbon steel that corroded. As the clip grew from corrosion it would eventually pop the end off the hinge pin. It's possible to drill out both the lever and the body a few thousandths and replace the pin with a SST welding rod pin or stove bolt.
Newer SP buckles use a peened pin and a slightly modified body.
Other SST buckles are available with a pin hinge, and are made of SST. The ones I carry are "good" stainless with a peened hinge pin. The metal shape is the same as the older SP buckles, but it has a better hinge than they did.
Both the SP and the ones I carry are "adjustable" for various belt webbing thickness. I have seen a couple others with pin hinges that were not adjustable for webbing thickness. I didn't try them so have no data on how well they'll work long term.
CUT HINGE
The least expensive metal buckles are 2 piece stamped metal deals where the hinge "pin" is a tab cut as part of the lever and is popped into place by springing the sides of the body out and letting the hole snap over the cut tab. Because the "bearings" in this design are simple lines of stamped edge metal the buckle wears out rather quickly Every one of the dozens of metal buckles I have recovered on lost weight belts had this type of buckle with worn "pins". I keep the lead and belt, but trash the buckles. The plastic buckles so common on 90% of the lost weight belts I've recovered are a variation on this theme with the "pin" molded as part of the lever. At least those can be used to make BTUs in a campfire.
WIRE LOOP
These consist of two wire loops that interlock when fastened and are retained on the ends of the belts in loops formed by two keepers. This is probably the most secure buckle and the fastest belt to put on. It is also a real PITA to adjust belt length or weights. If diving EXACTLY the same type of rig with the same belt they are great once you get them adjusted. If you regularly change exposure suits, or weight loads they suck unless you are willing to build a belt for each combination. I think Trident is the only one still making them, but they were common on equipment several decades ago.
FT
