I usually have to enlarge Dunlop large thumb picks by slipping them over the handle of a wooden spoon and holding it in a pan of boiling water - a few seconds at a time, until malleable enough to open them up a bit. I find the Dunlop preferable to the thinner 'Herco' type because there's more 'body' to the thumb pick so they don't seem to need to fit so tightly.
I also file down the 'blade' of the Dunlop to give a more pointed end - seems to give more 'twang'.
What an exciting life I lead
