When you sew with a treadle the leather belt stretches over time and needs to be shortened.
I have owned five treadle sewing machines and everyone needed a new treadle belt. If the belt was there it was rotton. The first time, I went to my local sewing machine dealer (Wayne) to buy a treadle belt, he insisted I borrow his treadle belt pliers. This little tool is the neatest thing it has a nail punch and belt cutter. First you open up the steel staple to remove one side of the treadle belt cut it shorter and then punch a hole in the new end. Put the staple back on, after trying it out to make sure it is the right length, squeeze the staple back together again. After I used his pliers I was so impressed with the ease of use, I knew I would never go back to using a hammer, nail and scissors to shorten my treadle belts again. When I reluctantly returned them... complete with my offer to purchase, Wayne said no, his Singer pliers were very old and not for sale. He did not think he would ever be able to get more.
Online internet shopping I go. I found them in the USA at at sewing machine parts place. I live in Manitoba, Canada. One pair was $25.99 plus shipping to Canada was $24.99 outragous! I decided that since the shipping was so much that I may as well buy two pairs, then gift the second set to someone else here who sews with a treadle machine. I paid approximately $80 US and waited impatiently for my new pliers to arrive.
Well I forgot that importing an item made in Taiwan from the USA to Canada is expensive. When Fedex showed up at my door with my package I had to pay another $38 in taxes, brokerage and duty fees. So here they are my two pairs of treadle belt pliers approximate cost $59 each.
Mine are way nicer than Wayne's because they are spring loaded.