I have gone through a few different brands of them in 7/8", one in particular has a spring on the pilot that keeps the cutter from crashing into the surface, (and knocking off the teeth) which does really seem to prolong life...

Speaking of which, 'long life', I usually use them at high speed and lubed which gets me through 200-300 holes on a single sitting with the average un-caring underling assigned the task. (Except for the one with the spring, still going on over 800 holes...) Should they be at low speed?

FYI I seem to buy one every sizable job... And give away the nearly toothless item when it's over. (Except the one with the spring...)

Mark Heller
"Well - I oughta....." -Jackie Gleason