We're not the first to point this out

but if you want a very low profile and low cost option to shiny metal knurls poking out the ends of your guitar strap simply purchase a pack of frosty cold Grolsch beer. After enjoying your adult beverage responsibly, prize the proud red washer off the top of the bottle and force it gently over the strap button while the strap is on the guitar. Works like a charm and won’t set off TSA weapon detectors. Reduce/Reuse/Recycle…that’s one of our mottos too.