Question about whitworth and platinum nipple

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From everything I’ve read I would need a 5/16x20 tpi platinum nipple for a Parker Hale Whitworth. I ordered one and it does not fit. I can’t get it more than a half turn before it gets stuck. Perhaps I need the 18 tpi? For anyone who has this rifle and platinum nipple what size did you use?
 
From everything I’ve read I would need a 5/16x20 tpi platinum nipple for a Parker Hale Whitworth. I ordered one and it does not fit. I can’t get it more than a half turn before it gets stuck. Perhaps I need the 18 tpi? For anyone who has this rifle and platinum nipple what size did you use?
Tap the hole to fit your new nipple.
 
Original Parker-Hale (England) use 5/16-18
EuroArms use 5/16-20 (M8x1.25)
A few early Euroarms where are assembled with original PH parts.

Measure the nipple that was in it?
 
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5/16-18 is a standard size thread.

5/16-20 is not.

Go to a hardware store and buy a 5/16-18 screw and see if it fits.

And re-tapping your bolster is a really bad idea at this point in the game.
 
Danger-Danger! Do not tap the hole to a different pitch but same size. Only re-tap when you can drill a new tap drill hole that cleans up the old threads. IF you run a different 5/16 pitch tap in to a 5/16 hole you will get nearly all compromised threads. The nipple will likely blow out.

The best practice for critical thread, like nipples, is as follows. Lock the barrel/bolster in a milling machine vice. Spot the hole with a center drill. Lock the x and y table feeds. Lower the table, drill one size under the tap drill. Clean up with the tap drill. Drills love to make oversized holes. Lower the table. Mount a pilot in the chuck to guide the tap. Tap. Make sure the tap is fully guided until it is well in the hole. Finish with a bottoming tap.

Do not free hand tap for a nipple in a bullet gun.

Agree, get a nipple that fits your gun.

IF a guy wants to work on guns you need a thread pitch gauge an a decent caliper. With those two you and identify any thread.
 
DANGER WILL ROBINSON!

I've retaped hundreds of holes for nipples! Without using $15,000 worth of machinery to do it!

Not only in breech plugs,lock plates or drums for muzzleloaders.
Rifle barrels, actions, engine blocks, boilerplate, centrifugal pumps, 2000 ton chillers and much much more.

One would think that before ordering just any nipple. To check the threads by using you know, maybe a couple little bolts or machine screws to get close to that thread size you need.

And Windex with Dawn will remove all your barrel seasoning!
SMH
 
Turn a piece of wood that you can thread into the hole. Measure the impressions with a thread pitch gauge. Check the minor diameter with your 100 piece drill bit set from Harbor freight using the shanks.

Print this out:
https://www.custompartnet.com/tap-size-chartLook up the various combinations. Figure what you got.

IF this is not some thing you are comfortable with that is fine. Take it to a machinist, preferably an old guy.

This chart ought to be a sticky. I have one stapled to the wall in the shop. I use it often.

If you randomly try screws in the hole you may buggar up the threads. That said try the 8mm suggested above, just be gentle. If a screw is correct it will go in with finger pressure and not wobble. 8mm and 5/16" are not the same.

I am not being a nanny or speculating. Bullet rifles operate at much higher pressure then other MLs. The pressure is way up there, like the long center fire BP rifle cartridges. About 30K psi. That is double a patch ball gun. IF you mess up the threads you could have the nipple blow out and the shooter suffer serious injury, or worse. Bullet rifles are serious stuff.

My mill cost $500.
 
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