"PrecisionmachinisT" wrote in message
news:cq2dnU9ZJ5D_ibHPnZ2dnUVZ_vGdnZ2d@scnresearch. com...


I've had most of the common tap drill sizes memorized nearly forever
anyways although frequently I'll use a slightly larger size, depending on
the actual job

Same here, a larger hole makes hand tapping so much easier and cuts
down on tap breakage.

A common internal thread, drilled so that it results in 50% of full thread
will break the external thread, before the internal thread will strip. A
common internal thread drilled out so that it contains 100% of full thread
is only 5% stronger than a 75% height of thread, yet it requires 3 times the
power to tap.

http://www.kennametal.com/kennametal...rill-size.html

Best Regards
Tom.