<br /><br /> http://www.engineersedge.com/tap_drill_chart.htm
But I really think we're splitting hairs since it's really gonna depend on how much he runs that tap in.<br />Dammit, is it just me, Starrett and my Busy Bee Tools poster that agree on that? I agree , between the two sizes is splitting hairs when it comes to decimal size and the criticality of tapping a hole to recieve a 1/8" NPT nipple.
<br /><br />Actually the USA now incorporates all standards of thread sizes and has for years.Just that our original national standards are still one of the standards.Sorta like gallons and litres.Or is that liters? <br /><br />Besides ,metric bolts in my Evinrude just wouldn't be right. <br /> it also depends on the materiel to be tapped and whether or not its a tapered,sealing, or straight,non-sealing pipe joint. <br /> the shift cable in the merc bell housings are modified from fwd entry to aft entry with a 1/4-14 straight NPT. I also use it to chase the threads after I have to drill out the snapped off cable.<br /> there is a book about 200 pages long describing thread sizes and standards, I machined class 3 threads for mny years as well as metric,buttress,acme,stub acme, pipe and a host of other oddball stuff.