View Full Version : Tap drill size

Jay Jolliffe
01-09-2009, 4:40 PM
I tried looking it up & it came up with various sizes for different threads? I need to drill out the sight plug on my furnace. I can't believe that on this furnace which is a Bock, which I would never buy again. You have to remove this plug to see the burner flame so the air can be adjusted. The plug is 3/4 with pipe threads. Does anyone know what the final drill would be before tapping.

Sonny Edmonds
01-09-2009, 4:50 PM
I found this (http://www.engineersedge.com/manufacturing/pipe-tap-drill-chart.htm)for you.
It sez 59/64's, to be exacery.
Unless you are using electrical conduit (straight pipe sizes), then it's 15/16's.

Put some Never Sieze (http://www.neverseezproducts.com/?gclid=CMG5qre-gpgCFRKLDQodkTwFDQ)on it when you get it fixed so maybe it won't stick again.
Or a brass plug even.
Sorry you got such a booger to deal with. :(