5/16-27 threads

I was looking to buy some bore cleaning brushes to clean out small holes, have some in .38 cal. Well I found out the larger shotgun bore
brushes have a 5/16-27 thread on them, thought this to be very strange, the smaller ones are a standard 8-32.
Where did a 5/16-27 come from? common on other gun stuff?
Good place to buy them cheap? or other small wire brushes to use instead of bore brushes?
Thank You, Randy
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MSC has that tap, HSS Special hand tap, plug 04841201 $14.44, bottoming 04841219 $14.44 these are imports, btw
gun screw threads are strange ducks, but, I dunno why this one is what it is
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Singer (the sewing machine people, who also have a repertoire of nifty industrial products), were legendary for their in-house oddball screw sizes/pitches. Which, of course, you had to order from them. Beautiful plated/SS screws, tho, often oval/filister headed, shoulder, etc.
Also, hazarding a guess, I think some oddball sizes were created here to match foreign/Bri'ish threads, and sometimes to serve as "jam threads", by just being a tad different from a std thread.
Just 10-32 and 10-24 throws me for a loop.... Also #12, 14 screws.... :)
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I suspect that just about anything with 27 tpi evolved from gas piping.
Back when homes were lit with gas, there was a lot of small piping needed.
A quick check shows 1/16 in nominal pipe had 27tpi and an OD of .313"
Sounds like the ticket.
Paul K. Dickman
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Paul K. Dickman writes:

Sure, but that just defers the questions as to why 27 at all? Market manipulation?
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Gas lighting was starting to spread while Maudslay was still inventing the screwcutting lathe.
My personal guess is that 27tpi is as fine a thread that men can reliably chase freehand.
Paul K. Dickman
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On Sat, 9 Aug 2008 09:31:43 -0500, "Paul K. Dickman"

I have run across a close approximation to 1/8 - 27 NTP but with 28 TPI, and since I was rejuvenating junk, I just ran the 27 TPI tap in and used a bit of extra pipe dope. Gerry :-)} London, Canada
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The Brits use 28tpi in the same small nominal size pipes. It also has a 55deg thread.
Paul K. Dickman
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On Fri, 08 Aug 2008 23:34:32 -0500, Richard J Kinch

==============That was the change gears installed on the lathe when the rush order for some 5/16 screws came in?
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    To discourage using homebrew devices in a safety-sensitive application is my guess. This eliminates using standard screws drilled hollow as fittings, since you can't find a standard screw at 27 TPI. :-)
    And in those days -- it was not just fire/explosion danger. The gas used did not have the butyl mercaptain (sp?) additive to give it an odor, so it was easy to be killed by a leak.
    Enjoy,         DoN.
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http://jtsmachine.com/jtswebshop/Taps_Dies/T058.asp
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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5/16-27 is a British, gas (brass pipe) thread. Might not be of any help though...
Mark Rand RTFM
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Mark Rand wrote:

Mark,
Are you thinking of BSB (British Standard Brass, although not as far as I am aware a BS standard) which is a 26 TPI constant pitch series with 55degrees Whitworth form and often confused with some of the 26TPI members of BSC which uses a 60 degree thread form. I looked up BSP yesterday but thread of this size in BSP use 28 TPI.
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wrote:

It may be an American 1/8" NB pipe thread. That has a 27 TPI pitch
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    Common on lamp sockets and the tubes which carry the wires to them. I think that they were originally the thread on indoor gas lights.
    And 5/8-27 is a common microphone mount thread.
    Some lathes with quick-change gearboxes can cut 27 TPI (like my Clausing), some can not (including at least *some* South Bend lathes).
    Of course pretty much any lathe with manual change gears can be set up to cut that.
    Enjoy,         DoN.
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1/8" NPT threads, shotgun cleaning rods, the copper pipe on Victor torch rosebuds are the 27 TPI applications I've run into. No idea where it actually originated. My South Bend won't do it. I'm sure some lathes will, I just haven't seen one.
Bill
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Pipe threads would be rough on a lathe - having to do it on a taper and having the cutter perpendicular to the face.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
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Yup, that sounds like an 1/8" straight pipe thread which is a variation of the more common tapered pipe thread. You should be able to screw it to any standard 1/8" pipe fitting. So, I'd wager they were using standard pipe as the rod and using a standard pipe thread for the connections. Why use an odd thread pitch on pipe threads? Perhaps to prevent people from attempting to screw standard fasteners into the tapered threads. That would deter folks from trying to cap a pipe with a standard screw, which would not seal well due to a lack of taper.
If memory serves me, garden hose threads, which are referred to as 3/4" GHT, are 1 1/16 by 11 1/2 TPI. Now there is an oddball thread...
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Enco 319-6373 $14.27 for the plug tap, 319-6469 $13.96 for the die. They also have 1/4-80 if you ever need one. The few things I've bought from them recently were good quality.
The South Bend 10L can cut 11-1/2 and 27 TPI.
Jim Wilkins
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