Tweco clamps come with a thin piece of copper that you wrap around the stranded wire. You should be able to find some shim stock at a hardware store to use.
I recently had to re-terminate a plug. The connection was getting warm. I had tinned the copper with solder before tightening it down. Tinning was a mistake as has been discussed here. I will not do that again. I cut a strip from a piece of copper tubing to use. It was a little soft. Will try copper pipe next time.