11 replies to this topic

[kilroyjones]

Could someone tell me if the Kahr 27's use the square thread on the chamber end of the barrel? What size is the thread used? Thanks.
Kj

[deerslayer]

All thompsons use the same barrel thread size (that is the same square thread as your question). I don't know exactly what it is, but PK should know.
Dan

[Bisley45]

Square, just like 03 Springfields and P14 & M1917 Enfields. Think that would be a good use of a Khar or W/H barrel except it be a louse use of an action.

BB

[PATHFINDER]

QUOTE (PhilOhio @ Oct 6 2005, 11:24 AM)

Aren't those called "Acme" threads?

You are correct sir.

[kilroyjones]

Square threads have a sharp 90 degree edge. Acme threads have a slight 45 degree bevel. Most vises and C-clamps have an Acme thread.

Thanks to everyone who replied. KJ

[amafrank]

There is indeed a Square thread as well as Acme, sharp V, truncated V, buttress.....the list goes on.
The thompson is a Square thread and I believe the pitch is 10 per inch. I can't remember the diameter though 7/8" comes to mind.
Acme threads don't have a 45 deg flank but they do have some taper where the square threads have very little.
Frank

[PK.]

How did I miss this thread?

Yes, Thompson thread form is what we call square, the major diameter is .848 and 10 pitch is correct.

Acme threads are 29 degrees.

[cocoabill]

I would like to chase the barrel treads of a 1928 receiver, I have my NOS barrel does not want to go in and I don't want to force it. 

 

Does anyone know a source for the bottoming tap this would require?  Looks like 7/8-10?

 

Thanks

Bill

[ron_brock]

Barrel to receiver threads are cut in a lathe and youre not going to get a tap or die. They are square threads like an Acme thread. Best bet would be fine sandpaper or lapping compound if something is not to spec.

It may help to clarify the problem who made the receiver and who made the barrel?


Ron

[1952HRA]

If it comes down to it I would do what Ron suggested, put some lapping compound on the threads and run the barrel in and out of the receiver a couple times (that's the process of barrelling bolt guns and M14 style semi autos with tight threads so I wouldn't see why it wouldn't work for a Thompson)

[cocoabill]

Thanks, I did not think of that.  These are both mill spec pieces, the barrel is new but the old reciever got a bit torn up and galled removing the old barrel.  Appreciate the help.

 

Bill

[giantpanda4]

I have found several "NOS" barrels that are slightly oversized. They needed to be just skimmed a bit and they fit fine.