7/16-27 NS Threads - Used for What?

[SouthBendModel34]

Forgive me if I asked this question before - I recall asking about an oddball threading tap, and I wrote the response on a pice of masking tape which I put on that tap. Said tap is misplaced....this is a newly-acquired one, and I think it is different. )

Found another oddball tap marked as follows:

Regal
7/16-27 NS
HS G331 <<<HS is obviously High Speed. What's "G331"?
6N ME <<< Any idea what these mean?

Note that it's 27 tpi, whereas the "EF" Extra Fine for 7/16 is 28 tpi

The 1946 (13th Edition) MAchinery's Handbook shows 7/16-27 listed under "American Standard Limits for Cut-thread Fractional-size taps", where it is listed in the NS column (NS= "Special threads with the Americal National form.")

7/16-27 is also listed as a Gas Fixture die size, "For fixtures and thin brass tubing"

The tap came to me in a big hip-roofed tool box that contained some "clues" that it might have belonged to a welder or steelworker. (A Flea Market purchase.) There were some OA torch tips and some drift pins, the kind used to line up bolt or rivet holes.

There are no boiler or staybolt taps sizes that small, although 27 is a standard pitch for staybolts.

What trade uses size 7/16-27 ?

Thanks - John Ruth

 

[Dave A]

John - Can only respond partially to your question. I do know that the 7/16-27 thread was used on the lead screws on Hardinge Cataract milling machines. I thought it was just sort of a joke that Hardinge pulled on unsuspecting machine purchasers some seventy years later.

Dave

 

[sinned]

isn't that 1/8" straight pipe used on lamp fixtures?

 

[HelEx]

Screw together microphone connectors - the old style where the central core connection is made by blobs of solder and the shield is connected with a loose ring. I'm certain about the TPI but may be wrong about the diameter..... I don't have one to measure.

- Mike -

 

[L Vanice]

Electric lamp tubing and nuts are 27 TPI and come in several diameters, but are usually 1/8 NPS. I suppose the practice goes back to 1/8 pipe gas light fittings. The finial at the top of a lamp harp is 1/4-27. A microphone thread is 5/8-27.

Larry

 

[Jim Williams]

From my 5th edition of Machinery's Handbook: (direct quote from text) Gas Fixture Threads.- Thin brass tubing is threaded with 27 threads per inch, irrespective of diameter. The so-called "ornament brass sizes" have 32 threads per inch. The standard sizes of the thread are 0.196 inch (large ornament brass size) and 0.148 inch (small ornament brass size). (end of quote). I don't know what the dimensions relate to, unless it is the thread length. Sizes range from 0.148 to 1 inch nominal size. The two smallest are 32tpi, with the rest all 27 tpi.

Jim

 

[SouthBendModel34]

Thank you all. From the context in which it was found, with welder's stuff, I suspect this is in fact a gas fixture tap.

Follow-up question:

"Bicycle Threads" - Isn't there an obsolete system of threading bicycle parts at a constant tpi regardless of diameter? What tpi? Is this British? (Meaning, would you see this on an old US-made bike, or only on a British-made bike?) If British, is the thread angle at 55 degrees like Whitworth or is it 60 deg.?

John Ruth

 

[Richard Rogers]

I seem to vaguely recall coming across that thread on brake line fittings??

Richard

 

[Jim Williams]

Same Machinery's Handbook lists: (quote) Cycle Institute Standard Thread.--This thread is made with a 60-degree angle and rounded at top and bottom. The depth of the thread equals the pitch X 0.5327; the radius of the round at top and bottom equals 1/6 of the pitch. (end quote) The number of tpi varies according to the size, which starts at 0.056 inch diameter and 62 tpi, to 1 1/2 inch at 24 tpi. The last four sizes, from 1.290 inch through 1.5 inch, are all 24 tpi. I thought it interesting that the 0.250 inch diameter has 26 tpi.

Seems that every industry had their own thread system way back then. Sure good that ASME consolidated things back some time ago.

As an interesting related subject, I was doing technical service work in Bulgaria in the late 1960s and needed to adapt some air system plumbing to the Bulgarian stuff, which I assumed to be metric. After a bit of fumbling around, I found that they, and presumably a lot of other European countries, use the inch pipe thread system. I understand that most of the early plumbing stuff originated in the USA and they continued using the thread system to assure later fit-up. We got our early spark plugs from Germany and got stuck on the metric system for them for the same reason. In Bulgaria they were using straight pipe threads which were hard to seal. I gave the plumbers a few rolls of teflon tape after watching them seal water pipes with straw and white lead. The teflon tape became a popular item to hand out on subsequent visits.

Jim

 

[franco]

S B 34,

Table of BSC (Cycle) thread pitches and particulars here:

http://homepages.tesco.net/~A10bsa/bscbot.htm

Most of the common smaller sizes are 26 TPI. They do turn up in unexpected places. I recently started restoring an old (30s or 40s) JAP industrial engine. The head studs on this are 5/16-26 BSC. Since J A Prestwich built motor cycle engines for many years I suppose this is understandable, but I was not expecting to find BSC on an industrial engine.

franco

 

[BernardC]

7/16"-27 seems to have been used on thermocouple connections to automatic fuel-gas valves on furnaces and boilers. 10mm x 1.0 is the metric version.

 

[Joey Novak]

Grease Guns...

I realize this is an old thread, but to add one more thing. Some grease guns use a 7/16" x 27 tap for the hose / pipe. (I think 1/8" NPT is more common).

 

[daryl bane]

Follow-up question:

"Bicycle Threads" - Isn't there an obsolete system of threading bicycle parts at a constant tpi regardless of diameter? What tpi? Is this British? (Meaning, would you see this on an old US-made bike, or only on a British-made bike?) If British, is the thread angle at 55 degrees like Whitworth or is it 60 deg.?

John Ruth

Strange as it may seem, but BSC (British Cycle) is a 60 deg thread angle, whereas BSF, BSW are 55 deg.

 

[john.k]

There are in practice two versions CEI ,which is the earlier one,for bicycles,and BSC adapted to motorcycles......BSC has mostly 26 tpi fittings ,some some axle threads at 20tpi..(Ariel was one)26tpi is too fine for axles ,but widely used in rigid frame ,girder fork days,even 1970s Triumphs sometimes had mixed threads on studs,SAE one end ,BSC the other.....cost cutting to keep older production machines in operation.BSC predates the BSF thread.

 

[Gordon B. Clarke]

Strange as it may seem, but BSC (British Cycle) is a 60 deg thread angle, whereas BSF, BSW are 55 deg.

When you're right you're right

Bicycle Screw Thread DIN 79012

I'll also add this to show how unusual some threads are.

BSB British Standard Brass

Have fun with this:

International Thread Standards