Trigger guard screw thread size

[John from the Cereal City]

I want to freshen out the threads on a Krag reciever that I have. As near as I can tell, they appear to be a 1/4 x 24 thread size. Is that correct? It looks like I will need to purchase a special tap and would like to get the right one.

Information

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[1886nut]

If the threads are just dirty you can clean them out with aome Kroil and an old .32 caliber bore brush that has had the metal tip ground down flat so you can get in in the hole on a drill set on slow.

if the threads are boogered you can sometimes make your own "cleaning up" tap with a screw that has had the thread lead carefully squared up with a Dremel. Heat with a torch to cherry red and then quench in some dirty motor oil.

[chuck in idaho]

John,
The guard screws have a pitch of 25 threads per inch. Diameter of treads were 0.25"
Remember Krags were made before the U.S. started using standardized thread sizes.

HTH
Chuck

[Texasflyboy]

John,
The guard screws have a pitch of 25 threads per inch. Diameter of treads were 0.25"
Remember Krags were made before the U.S. started using standardized thread sizes.

HTH
Chuck

Last year when I measured my original sideplate screw and trigger guard screw my Starrett thread gage said 26 tpi, which is an obsolete screw pattern. Virtually impossible to find taps or dies in 26tpi in the Krag screw sizes. I used a 10X loupe to pick the best fit and 26tpi won. If the drawings say 25tpi, or Chuck has a reference, I defer to his expertise.

24 tpi, which is very common (#10 for example) is close enough, but if you choose to clean those 26 tpi threads with 24 tpi cleanout tap, you will press over the threads for the last 50% of thread as the mis-match increases. You probably won't ruin the threads, but the maximum sustainable torque will be reduced dramatically.

I would clean the threads with solvents, and/or soft bristle brushes and not use a tap unless you can find a 26tpi tap in the size you need.

[chuck in idaho]

Texasflyboy,
Good point, side plate screws are 26tpi. So are the upper and lower barrel band screws.
Krags and 1903's used simular length front and rear T/G screws, both with the same pitch of 25 tpi. The 25 and 26 tpi information I used came from 'The Krag American Rifle and Carbine' page 110 and 'Manufacture of the Model 1903 Springfield Service Rifle' by Colvin and Viall.
I find it interesting that Springfield would use 2 tread pitches so close together in size.
Thank you for your input. Input like this helps us all learn.
Chuck

[John from the Cereal City]

Didn't have any Kroil, so I put some liquid wrench in the holes & let it set a day or two, then using a .22 cal bronze brush, I twisted it around several times. The trigger guard screw goes in nice & easy, no gritty feeling.

[Dave]

when faced with a prolem/question like this call Brownell's. They can probably answer and may even have what you need. I was faced with same question on 98 Mauser's, thought it would be m/m, lo and behold it is 1/4 20. Every other thread on those guns are m/m! Also Brownells 'Encyclopedia of Modern Firearms' is loaded with this kind of info, altho seems to just cover civilain rifles and pistols, some military shotguns.