The treadle sewing machine belts are held together with a piece of
wire.  It's almost as hard as piano wire.  The belt will stretch for
a while so you need to shorten it now and again until it finishes
stretching.  You can use what you cut off the sewing machine belt to
replace the worn out leather on your Victrola brake!

A friend of mine here in town has a Eberhardt nickelodeon that still
has the original belt on it, and Terry's belt has a wire holding it
together at the splice.  Actually his piano is unrestored and still
plays quite well after 101 years, but it's getting to the point where
he needs to go through it.  I helped him remove the pump a few years
ago and looked over the belt then.

Good luck with your piano now,

Earl Hennagir