What is this arse buckle for? (photo)

[Vitamints]

I've managed to identify all the other random bits dangling off these jeans (tool accessory pocket, hammer loop, turnup strap buttons) but have failed to divine the purpose of the arse buckle. Any ideas?

To tighten up to prevent builders arse?

Hmm. It's possible. I've tried tightening it to its fullest extent and it doesn't seem to make an appreciable difference to the fit. Perhaps a little snugger in the upper buttockular region.

I believe it's called a cinch. They had them on jeans before belt loops to tighten the waist but now they are now just a fashion detail. They are a throwback to the 1890 (maybe) levis edition of jeans had cinch and buckles for braces but no belt loops.

Thanks Clara. That's really interesting and makes sense as a sort of vestigial thing, or rather a throwback detail. I've just realised that I've actually seen one before on dungarees, I guess because dungarees look kinda daft with a belt.

I knew someone would know a better name for it than arsebuckle

Arsebuckle did make me LOL. I may use that in future...