I got a couple chrome 1/4" x 7/8" washers to use as strap-locks with the standard Gretsch Electromatic strap buttons. They work great. Three bucks! | Gretsch-Talk Forum
Strap lock users | Gretsch-Talk Forum
How To Use Gretsch Vintage Locking Strap Buttons - YouTube
Gretsch Guitars Schaller Strap Lock Button | Music & Arts