[mattbacon]

Thanks, George... sorry, I should have said. I heated the plastic very carefully under the gas grille on my oven. Hold it a 10-15 cm below the grille, and you can see it warp slightly and then sag into the hole. Then it's ready. Push the master through firmly but not too quickly, and you'll feel it suddenly "give" and stretch. Practice and experiment with what works for your plastic -- too little heat and it won't stretch far enough to mould to the master; too much and it'll spoil the plastic and ultimately catch fire! I threw away three failed ones before I got on a roll with these...

bestest,
M.