thread size measurement

pj1

Well-Known Member
Hi all. I have just acquired a new rifle and was assured that it had a 1/2 unf thread. Lovely I thought that will fit my mod i have already. Tried fitting it tonight and low and behold its the wrong thread size.
So is there a way of measuring the thread without buying a special tool if one even exists.
I have measured the screwcut section and from crown to face where the mod should stop is 14 mm. Is this measurement of use or do I need a diameter or count the threads etc.

Also if a rifle is factory screw cut and then proofed is there a proofing stamp just near the action. Or if it is after market screw cut and then reproofed is there a stamp on the muzzle end of the barrel.

All in all I'm a bit miffed as I was told it was factory screw cut ( not sure it was ) and half inch unf.
Needless to say the dealer will be contacted. But in the mean time thanks in advance for your help.

Also can I buy a different thread section for my a tec mod

Regards Pete
 
Last edited:
It could still be 1/2 UNF

maybe 1/2 x28 rather than 1/2x20 there's a few 1/2 threads used on muzzles but not sure of all of them

if proofed after threading yes proof marks by muzzle
 
Sorry to hear about the issue, what gun is it on. If its American like a Winchester, it could have a 1/2" UNEF or 28TPI.
 
If the rifles been sold to you and the previous owner had it screw cut it has to have been proofed before sale.

The PH usually mark the barrel at the shoulder of the screw cut (though not always)

Easy to check thread - measure the diameter - if its .500" (1/2") then the thread will either be 1/2 x 20 Tpi or 1/2" x 28 Tpi (1/2" UNF or UNEF)

You need a thread gauge to check this though (the TPi)

It could be M14x1mm again - determine this by measuring the outside diameter of the thread.
 
Last edited:
1/2" outside diameter thread options ---

UNC = 13 TPI (Threads per inch)
UNF = 20 TPI
UNEF = 28 TPI
BSW = 12 TPI
BSF = 18 TPI


Metric coarse threads
12 mm outside diameter = 1.75 mm thread pitch
14 mm = 2.0 mm
16 mm = 2.0 mm
18 mm = 2.5 mm
20 mm = 2.5 mm

Metric threads are often cut to different pitches to these standards so beware of that!

Take your pick!

Diameter is easily measured with a vernier caliper or micrometer
Thread pitch / TPI are measured by using profile gauges - or by measuring the distance a nut travels along the screw when it is turned once.
Go play!
There is no substitute for measuring the items you want to fit!

To complicate things some numpties can't use tools properly & machine threads badly & to wrong dimensions! - watch out for those!!

Ian
 
Last edited:
Thanks for all the replies. I will measure it again tonight. What has really wound me up is I bought a Schmidt scope for the rifle as I thought I wouldn't need a different mod. So now don't have the money for another mod and as I use the atec on my hornet it would mean buying two mods if I get rid of my atec due to different thread sizes
 
well the thread seems to be 1/2 inch diameter but as the photos show it just doesnt want to fit. the three threads left to right are weihrauch, cz 452 and then the cz 557.
View attachment 49372View attachment 49373

these photos show my a tec .22 mod which geos on further but as can be seen from inside the mod it also runs out of thread
008.jpgView attachment 49375

ive counted the threads at a set width and they are all the same. has anyone else had this sort of problem. seems to be right thread but to much of it.
 
Last edited:
Does it screw all the way on the 1st (weihrauch) thread ok? That looks nearly as long to me.
it could just be a carbon build up in the moderators threads, running a tap up the mod might work but it would be nice to see what it stops on before doing anything drastic.
Has the mod been used on the centre (452's) thread which to me looks a bit short?
 
The mod goes all the way on to the weihrauch no problem. The lengths of barrel that's has been cut are 14 mm for the 557. 12 mm for the weihrauch and 11 mm for the 452. I haven't used the centre fire mod on the 452. I have cleaned the threads with a bronze brush but there just doesn't seem to be enough thread in the mod or there's too much on the rifle.
 
If you have a thread protector then take that to your local DIY or hardware shop and find a bolt that it will screw onto - that will be the thread, easier than carting the rifle around
Wingy
 
Thanks wingy. Less chance of getting arrested as well taking a thread protector into b&q ( other stores are available ) than ny rifle.
I phoned Edgar brothers today. They said they get them screw cut and proofed and the thread should be 1/2 inch unf
 
It's not really a thread that's used in many other applications so very unlikely to be found in a DIY shop.
Buying or borrowing a tap would be your best bet, they aren't very expensive. Most gun smiths would have one kicking about too, is the mod screwing up nearly all the way as the threads are only 2mm longer?
I would even consider trying a bit of force as its probably a carbon build up that is stopping it screwing on all the way, if you ask for a bolt you need 1/2"x20tpi
 
pj1 dont force the mod on you may cross thread it the your ****ed try and clean the threads but easier to check with both 1/2 unf threaded mods
 
Sorry bennyblanco that is bad advice! Especially when given to a non-engineer!

Forcing a moderator with any crud in the threads onto a barrel is NOT what you should do! - You are very likely to mess up the threads on the rifle & moderator doing that. Use a thread cutting tap to do it, & even then be very careful to align it right so that you don't get it cross threaded & ruin the moderator. Proceed slowly working in stages - screwing the tap in & then backing it off & blowing the crud out as you loosen it.
Taps are available online for about £5 - it isn't worth ruining either your rifle or the moderator for the sake of spending that!

Ian
 
The thread on the rifle is possibly on the large side. A 1/2"x20 die could be carefully run over. You'll notice right way if the die screws over the other two threads easily without taking off material and will probably cut some material off the tight muzzle. Better to re-work the problem barrel instead of making the mod thread larger as it might be very loose on the other rifles then.
edi
 
The moderator thread obviously has a build up of carbon on the unused threads.

The longer (new rifle) thread is tight where the carbon build up is - hence why it won't screw on.

Clean out the mod thread and i'll bet it will screw on fine.


Clean out with 1/2" unf tap
 
Back
Top