Going to be replacing my thimble that goes into a mason chimney.. need to do so because the one that was made before i bought the house is very low making it so that the stove pipe coming off the stove collar is a very very short run into the thimble. I will probably use Rockford Chimney Supply's Insulated Wall Thimble (round), my question is whats the best way to make the 6.25" hole cleanly through the brick AND the 3/4" clay liner. would a core drill work? im sure there is a concern on the liner cracking, but i assume a core drill would be best. also, if anyone has had experience with that company's wall thimble let me know how it went install wise and how you like the product. Thank you!