I don't have real many parts machines - I have a Singer 500 that has saved so many machines it isn't funny. I have a T&S that is recent and a couple Japanese machines - it amazes me how much will change over. It also amazes me how many different parts seem to be missing off similar machines so that one donor will do the job for many machines. Some times it is an itsy bitsy screw or spring or a slide plate or a part off a tension. I have rebuilt about 6 tensions in the last week. It is getting easy but sometimes I still have to look at another machine to be sure I have it back right.