unknown thread of this tap

Can anyone identify the fine thread on this tap, it's 5/8 X 56 NSVT

I can't find any ref to NSVT other than a medical condition

I wonder if perhaps it should read NSVF

… as in Very Fine

MichaelG.

.

Edit: __ “… the Unified series adopted by Great Britain and the United States during the war, and the corresponding American National Standard. NC and UNC mean coarse thread. NF and UNF mean fine thread. NS means special thread.“

Ref. __ https://www.newmantools.com/taps/taptech.htm

Edited By Michael Gilligan on 27/01/2022 16:58:01

Excellent idea to have the built-in pilot!

Fine thread

Steve.

You can get a die to match.

Edited By Bill Phinn on 27/01/2022 17:46:17

Thanks to all for your replies, it's definitely reads as NSVT but can't find a ref to it

NSVT is unlikely to be a typo but Iv'e never heard of it. What else is printed on the shank?

Tony

It could easily be a special made for a particular job. I have a box of specials at the museum, from the toolboxes left to the museum. If very unusual sizes were specified, a firm would add the tooling costs to the quote and a specialist would make it.

The NSVT may be a code for the job it was used on and nothing to do with threads.

 The threads on the tap look like a multi start on my screen, probably an optical illusion. I would 56tpi to look like rings turned. I turned a 40tpi on a 1.26" diameter today and I cannot detect any helix angle by eye.

Edited By old mart on 27/01/2022 20:35:53

A quick google search produced a US website selling 5/8-56 taps with a review stating "needed for gunsmithing", so maybe thats where this thread finds a use.

It might be for threading rifle bores looking at the long lead at the front maybe to fit a smaller bore possibility an airgun /rifle

Don't think so it's a bit too fine., 5/8 is a common barrel size but powder burners usually use 5/8 x 24 TPI to secure them to the action, can't think of any common airguns with a screw in barrel.

I’d have to go for Valve Thread.

Perhaps you are looking at the wrong end of the barrel. Could it possibly be used the thread the inside of a 20 Ga.shotgun to install removable chokes? Hust a thought. Rick

12 gauge shotgun choke thread size is 13/16” x 32. Dave W

NSVT is a tank mounted soviet era machine gun...

Oh I can see why Dormer 'England' made taps for it.

Tony

Just a thought....

Considering how fine the thread count is, I'm wondering if this wasn't a special tap for something in the camera/optical field.

As an ironmonger in the sixties or seventies Draper were selling of mixed lots of 100 taps, ex WD and by UK and USA makers, my cousin and I bagged the best ones for ourselves, but there were some very odd sizes and threads in the assortments. I still have a few, a 1/2"and 3/4" still in use for my garden irrigation projects!

So there a possibilty It may be for a milatary purpose.

The NS bit is easy enough: 'The NS series is a catch-all category for threads which have the American Standard form, but whose pitches are not in the National Coarse or National Fine series.'

Possibly VT indicates a particular purpose like 'Vacuum Tube', or it might just be a catalogue code. Or a property such as 'V-Thread', meaning the valley root is cut sharp rather than flat.

Fine threads imply strong joints or gas tight, or thin-walled. As NS suggests USA origin, but the tap is British, I think it was made for a UK organisation that imported a significant quantity of an American equipment and maintained it locally. Loads of possibilities - could be military, maritime, aviation, medical, chemical engineering, pressure vessel etc. Could be military except the absence of a broad arrow, pattern number or NATO Stock Number hints it's not.

Whatever it is, it's special.

Dave