This might sound goofy but it's what I tried and it worked for me. The thimbles I had kept coming off so I needed them to be tighter. I put on a pair of rubber medical gloves. Squirted some silicon sealant inside the thimbles then put them on my gloved finger and wore them til they dried. Then I cut off the rest of the glove and now they fit tight on each finger. Labeled with sharpie r1, r2, r3, r4 for each finger and did that for both hands. Works great and they don't slip. Of course I'm a perfectionist on everything but playing and I've got entirely too much time on my hands.