Help.....Trying to build a 1:35 scale pully

This is is probbably an amitures question, so please bare with me. I am building 1:35 an M40 155MM gun motor carriage from AFV Club. The assembly is somewhat trickey. Several small parts. I am using pic Stcks (got that info on those little sticks from this forum, geat little tool). However the model has some pullys that were quit fragile. I destroyed one durring this build. My problem is I am trying to scratch build a pully to scale. I have tried lots of different material, processes, and none have worked. I have tried plastic styren, buttons, (all too large), rubber gromets (size issues again). I am totaly stumped. I don't want to box it up and put it back on the shelf, I have come to far, and it is really taking shape. Can anyone please give me some fresh ideas, or guideince. The old guy is 63, retired and frustrated. I would like to thank anyone who responses to my delima in advance.