I used what I think is called a clasp pin, at least in some parts of the US.

Honestly I was hot for countersinking a couple rare earth magnets into the back of the pin and polishing up a piece of steel for the backside of the front apron, but something wasn't right. I finally read enough naysayers about magnets to see my self coming back to the party with a fresh beer in one hand no pin on my kilt....

I bought a package of these at a local to me craft store, epoxied in: