Back in 98 when my cousin gave me Singer 66 Treadle #1 we went to the LSMG and bought a nice 3/16" "Made in Japan" treadle belt. 13 years later it was still wrapped up in the drawer. When I finally put it on the machine I only had to adjust it once. A year later it's still there and working fine.
Those I've bought in the last year have been made in China and stretch, stretch, stretch. It's frustrating.
I've had to adjust the belt in 66 Treadle #2 three or four times, and in 9W-7 Treadle #4 I gave up on it and made a belt out of aquarium tubing.
The belt in my Franklin is a 1/4" belt and so soft I have to adjust it every time I use the machine. It came with treadle #4 but I needed it so it got put in the Franklin.
What I need to do is find the name and contact info to a gal who has 1/4" leather belting by the roll. Then buy a roll and make my own. One of the other members here gave me her contact info, but .... I've lost track of it again.
Joe