Tapping puzzler

Then they won't cut proper UN threads. The *minimum* major diameter for 1/4-20 UNC - 2B (and 1B & 3B) internal threads is .2500. Likewise, the minimum major diameter is equal to the nominal size (the basic major diameter) for all 1B, 2B and 3B UN threads. Similar rules apply to metric threads.

But not sharp sharp, just sharper than the mating external thread.

OK, many of my tools were second-hand. New 1/4, 5/16 and 3/8 taps measured 3-4 thousandths over nominal size. jsw

Forgive me if someone's already said this, but -- you can buy all sorts of brake line fittings. Tee joints should be easy. Even adapters from one thread type to another should be available if you're willing to mail- order from performance shops.

It's not something that I'd want to mess with, other than perhaps to put a notch in my gun-butt: "been there, done that, look ain't I competent." Having done it I'd probably never do it again.

Most..not all perhaps..but MOST NAPA stores have those adapters (at least in my area) and their website lists all kinds

You got me wondering so I checked some taps I have that are old enough to be marked "USS." USS threads were superseded by National (NC, NF) threads, which were in turn replaced by UN threads. Even the USS taps I checked, which happened to be Greenfield taps, had a major dia greater than nominal. What I don't know, because the oldest MH I have covers only National threads in detail, is whether the USS standard insisted on the oversize major dia.

Most of the required fittings are in stock at any reasonably equipped auto parts store. I can get just about anything from any of

NAPA always has the best price on custom made hydraulic hoses, too.