Regis, when i design and buid a guitar strap for a Professional Play
that strap is for one guitar only. These players use fastners refered to as
"strap locks" , this will give them the adjustment length they will need ,with
a coupla of extra holes to put the strap lock in on the end of the strap.
I do not use this 100% but most of the time. Most of my straps are
for the Heavy Electric guitars. the Accustic are light weight and i
will punch a keyhole slot for attachment.
Some times i will use a Large buckle on the front of the strap, like a
3 pc western style, and the billet end will give some amt of adjustment.
Do like i have done , check out a Music store to see the straps they sell
and then improve with your own touch.
(would send photos but ,they are too large, WE will fix that on the next visit?)