I have a VPI Aries II (12 Inch platter and 300Hz motor) After reading this thread, I made a belt for my Aries from 12lb Power Pro braided green line.
I ballparked the length of the Aries belt to be 40". Made a belt with a simple overlap knot. The belt is a bit short, I had to adjust my SDS to 63.28 HZ to get the right speed. So next try will be 41" long.
Seems to work well, speed is stable. Table sounds brighter now with bass tighter. I need to do more testing.
The VPI motors weight a lot and being standalone it is easy to adjust for a thread type belt.
The 12 lb braided fishing line. 0.10mm diameter is extremely small. In comparison, No. 2 silk thread is 0.45mm, No. 4 silk is 0.60mm, and No. 6 silk is 0.70mm.