Tap size questions

[torker]

G'day! Got another one for you! I just got another batch of taps from Ebay. Mostly BA stuff that I can't use but there are some weird ones as well. One is marked--- .4355X20 UNS Another---9/16 NS 12 then under that is..HSGG MAG +.12
594
Except for the name all the numbers/letters are hand written with a metal engraver like they mark tools with. Can anyone explain these strange numbers etc.? Thanks.
Russ

[3 Phase Lightbulb]

<font face="Verdana, Arial" size="2">Originally posted by torker:
G'day! Got another one for you! I just got another batch of taps from Ebay. Mostly BA stuff that I can't use but there are some weird ones as well. One is marked--- .4355X20 UNS Another---9/16 NS 12 then under that is..HSGG MAG +.12
594
Except for the name all the numbers/letters are hand written with a metal engraver like they mark tools with. Can anyone explain these strange numbers etc.? Thanks.
Russ</font>

Just guessing:

.4355X20 = Re-ground 7/16 20 threads per inch.
9/16 NS 12 = 9/16 12 threads per inch.
HSGG MAG +.12 594 = Re-ground 3.5mm

-3Ph

[Evan]

UNS stands for UNified Special. It can be whatever is needed and is non standard. NS same thing. I'm guessing the 9/16 X 12 is just that. The HSGG MAG +.12 is probably some in house identifier.

[This message has been edited by Evan (edited 01-05-2005).]

[torker]

Thanks guys! I wasn't aware that they reground taps. What would be the purpose for that anyway? Would it be to tighten up bolt /fastener clearance for some reason? I've run into the UNS before...seems a lot of automotive stuff uses this as we've discussed before. All the other info on the taps is what threw me.
Russ

[Rich Carlstedt]

I got some really weird taps over the years, and they have come in handy to..
Many ,many shops in the 30's and 40's made their own tooling, particularly during the war.
back then , they had real toolroom machinists and tool makers, so it was not a problem. they usually marked the major diameter and either the threads or pitch . Some of these custom threads were used for oversize holes for heat treating when shrinkage will close up the hole ( I have a .318 X 24 ), and some were used for "factory stuff" like Brown and sharpe, used 1/4 x22 threads (thats right !)
I have a .563 -.025 , which is really a 9/16 X 40 thread tap.
Had to make some when I was working...like the 5/16 NPT ? can't buy it, so we made it...Darn Enga-neers

[Ian B]

Torker,

The purpose of these taps is to give you the false impression that you have just the right tap for a particular job that needs finishing. This misconception is usually discovered on a Saturday afternoon, just as your local tap shop is closing.

The sizes are close enough to tempt you to use them anyway, resulting in you ending up seizing the male threaded part immovably in place, hence scrapping your otherwise finished workpiece.

During the futile attempts to separate the pieces, it's usual for the pipe wrench (which by this time you'll be using) to slip and remove several layers of skin from your knuckles.

These taps are invaluable - I have several...

Ian

[SGW]

"The purpose of these taps is to give you the false impression that you have just the right tap for a particular job that needs finishing. This misconception is usually discovered on a Saturday afternoon, just as your local tap shop is closing."

Been there, done that.... A while ago I picked up a bunch of surplus tooling at $5/lb. that included a whole mess of small taps. When inspected in the comfort of my shop, a high percentage of them turned out to be NW -- National Weird.


[This message has been edited by SGW (edited 01-06-2005).]

[3 Phase Lightbulb]

<font face="Verdana, Arial" size="2">Originally posted by torker:
Thanks guys! I wasn't aware that they reground taps. What would be the purpose for that anyway? Would it be to tighten up bolt /fastener clearance for some reason? I've run into the UNS before...seems a lot of automotive stuff uses this as we've discussed before. All the other info on the taps is what threw me.
Russ</font>

I was just guessing about the "Re-ground"... The Machinist's Handbook has a really good section on threads and shows 3 standard tolerance ranges for each tap size. My guess was that you could "In theory" re-grind a tap to get to the next tolerance. I did sleep at a holliday inn once..

-3Ph

[torker]

Hahahaha...funny stuff guys! I just can't wait to bust a bolt off in an under sized hole! So the secret must be to wait until after lunch on Saturday after Stronco is closed....then git after it and bust something. What a buy!!! Ya gotta love Ebay sometimes! BTW..If you talk nice I might have a bunch of NW taps for a VERY good price. Then you too can amuse yourself on the weekend!
Russ

[CCWKen]

If you're into restoring antique autos, some of those "bastard" taps come in handy. I spent a couple of weeks looking for a #14-24. Not to mention the stinking 3" brass screws that go in the holes.

I'm still cussing the idiot(s) that came up with all the different hydraulic fitting sizes. Geez, what a mess.