Machinist's riddle...

[MultimediaMan]

I'll grant you it isn't common anymore, but it used to be quite common as a "trades" screw for certain items, particularly in older tooling and automotive applications (Carburetors, distributors, precision parts of larger machines). In Aerospace, it still has a following among certain aircraft engine manufacturers - Lycoming and Pratt & Whitney.  I remember my dad running across the street to the lumber yard to buy some #14 - 20 taps and dies when announced it's removal from the official SAE series... about 1985, I think...

Anyway, here they are, still in the wrapper, about 30 years later...



Eventually, the 1/4" - 20 was the preferred standard across "disciplines", leading to the decline of the largest end of the numbered screw series during WWII and after. Most people who use #14 - 20 today do it to prevent common (untraceable) 1/4" - 20 fasteners from being used for a particular reason - so they still have a place, crazy though it may be.

[willbird]

I actually have a 14-20 tap in it's proper drawer (with the number taps) out in the shop :-).

[JJXGRUNT]

Regardless which volume of "Machinery's" you are looking at, the table will be in the chapter regarding tapping.

John

[HYspd]

that's not a riddle that's history or trivia..THIS is a riddle.

how much lead would a lead screw lead if a lead screw could lead screws

[Roadworthy]

That was an interesting bit of trivia.  I did a web search and found there was such a thing and it is still supported, though not very common.  Thanks for sharing.  I am now a wee bit wiser with arcane information and trivia.

[OleTomCat]

8-32, has a larger cousin 10-32, which can be mistaken for an M5 or 6 don't remember which...

5/16-18 can be mistaken for an M8.....

Just some fun facts...