I think it's trial and error. I keep trying different thimbles, but seem to keep going back to the leather coin thimble that I can get at JoAnn's. It's $13, but I will pick them up when I have a coupon. The coin thimble is leather and has a little metal piece w/ dimples that is round that covers the pad of your finger. I wear it on my middles finger on my right hand (i'm right handed.)