Bullet twist pen any one know the transmission thread size

Signed-In Members Don't See This Ad

Alpha1

Member
Joined
Apr 8, 2018
Messages
8
Location
England
Probably been asked before but can anyone help I am trying to make a pen out of some bullet cases I need to make a longer holder for the transmission anyone know what the threads are.
 
Signed-In Members Don't See This Ad

magpens

Member
Joined
Feb 2, 2011
Messages
14,240
Location
Coquitlam, BC, Canada
@Alpha1

Have you measured the diameter of the threaded part of the kit that you want to replicate ? . You would need calipers to do that.

The additional info needed would be the pitch of the threads.

I expect the diameter would be in the 6mm - 7mm range. . And I expect the pitch would be about 0.4mm - 0.5mm

Of course, you need an exact match. . I will try to find some examples of this construction in my stash of stuff.
 

magpens

Member
Joined
Feb 2, 2011
Messages
14,240
Location
Coquitlam, BC, Canada
OK ...... I have found a pen with a very similar construction.

It is a PSI pen kit .... Classic Twist .... Here is a link :-


I measure the diameter of the threaded coupler for the twist mechanism ..... measures as 6.8 mm

The thread pitch seems to be 0.5 mm ...... bear in mind my aged eyes trying to use a thread gauge !!!!!

So I would say THIS thread is .... M7 x 0.5 .................. but YOURS may be different ........... I don't have your exact kit to measure from.

I have found Berea to be very helpful in the past. . So if you were to send an email asking who to contact about the threads on YOUR kit you just might get a referral to a person who would know the info you need. . I have forgotten the name of the person I spoke to ... I think first name was Jim
 
Last edited:

magpens

Member
Joined
Feb 2, 2011
Messages
14,240
Location
Coquitlam, BC, Canada
Another example of similar threading on a pen kit twist mech .....

I found another kit with similar threaded twist mech ..... but this one is "reversed" ..... twist mech has male thread.

This kit is the PKCPEXPR .... or .30 Cal Express Pen Kit ..... from ..... woodturningz.com ..... will try to give a link at the end of this post.

THE IMPORTANT THING is that the thread size appears to be the same as I mentioned above .... namely M7 x 0.5 (close as I can "measure")
My actual measurement was a diam of 6.8 mm, with pitch of 0.5 mm

I am pretty sure that if you emailed the owner of WoodTurningz he would be able to give you the thread specs. . Quite a helpful guy.
I might remember his name in a day or so (sorry !).

Here is the link :- https://www.woodturningz.com/30_Cal_Express_Pen_Kit (check the instruction sheet for diagram showing twist mech)
 

magpens

Member
Joined
Feb 2, 2011
Messages
14,240
Location
Coquitlam, BC, Canada
Here is YET ANOTHER example for your consideration. . But I don't think it is a match for your pen kit.

It is the Berea Cigar Pen kit ..... here is the link :- https://www.bereahardwoods.com/pen-kit/sets/cigar-pen-chrome.html

I have done a lot of work with this particular pen kit. . But for some reason I had a mental lapse until a few minutes ago.
It has similar architecture to yours ..... twist mech screws on in a similar way.

Only problem is that this kit has bigger thread OD ..... measures at 7.3 mm, so I suspect the spec is actually M7.5 x 0.5 mm
Twist mech has female threads; coupler piece has the male threads (which I think is the same as yours).

So, while not fully compatible with yours it may be an example to keep in the back of your mind.

Many companies sell this style of pen kit (some "better" than others) and you should be able to find in the UK if you should ever want to.
I really like the general features of this pen kit styling. . The Berea model which I have referenced is probably the best available for smooth operation and reliable plating options.

I hope that some of the info I have provided in the above 3 posts will be interesting and/or useful to you.

Please keep in touch and let me know what you come up with for your project .... also feel free to send along any questions you may have.
 

Alpha1

Member
Joined
Apr 8, 2018
Messages
8
Location
England
Thank you very much for taking the time to reply. I am trying to modify a transmission to create a bullet pen using original casings problem is the cases are short so I need to make the transmission longer. Finding the right tap size has proved very difficult. I think you might be right about the M7.5 x 0.5. I have ordered some taps in M7 X 0.5 and M7.5 x 0.5 I will let you know how I get on when they arrive. Thanks.
 

magpens

Member
Joined
Feb 2, 2011
Messages
14,240
Location
Coquitlam, BC, Canada
@Alpha1

I feel that M7 x 0.5 is more likely the correct thread, but I could be wrong because I have not had the pen parts in my hands.
From country to country (vendor to vendor) there can be differences in kits, even those marketed with the same names.

There is one other thought I have had, assuming that what you want to do is basically to extend the twist mechanism a bit .....
..... if you have an alternative method for refill replacement that does not involve unscrewing the twist transmission.
You could make up a short tube of the appropriate length/diameter and glue it to the existing parts with 2-part epoxy.
To do this, I would recommend doing any parts modification/fabrication with a metal lathe, but a wood lathe might be "up to the job" using suitable cutting tools and taking suitable care.

Looking forward to hearing about your success !! . . Good luck !!
 

Alpha1

Member
Joined
Apr 8, 2018
Messages
8
Location
England
Hi again
I am lucky in so far as I have a small workshop with a metal lathe a wood lathe and a milling machine. I am more at home with a metal lathe I do most of my pen turning on a metal lathe. The taps should arrive sometime next week. I will keep you posted. I need something to cheer me up I spent today in my shop I had two expensive blanks blow up on me. Another pen I had to fight with all the way to the finish only to find the bushings were undersized so hangover at both ends of the pen. One step forward and three steps back. Why do we do it.
 
Last edited:

Alpha1

Member
Joined
Apr 8, 2018
Messages
8
Location
England
Just an up date.
The thread is M7.5 x 0.5.
At first I thought It wasn't I tapped a 8mm tube but it was a loose fit on the male part it screwed onto but what had happened because 8mm pen tube walls are so thin the tap bulged the tube slightly resulting in a sloppy fit.
I asked a machinist friend to measure the thread and he came back with M7.3 X 0.5.
So I started again I cut some 8mm brass rod into 4 inch lengths and put a piece in a four jaw chuck on the metal lathe. I drilled a pilot hole then worked my way up in drill sizes until the internal diameter was 6.5mm I then switched to reamers starting with a 6.6mm and worked up in increments to 6.79mm. I then ran a M7.5 x 0.5 tap into the tube. I cleaned it up and screwed it onto the fitting on the pen kit and it fits perfectly. So Cigar pen and bullet twist pens kits threaded bit the transmission attaches to is M7.5 x 0.5. I can now crack on and make my custom pen I have had on hold whilst working this problem out. Thanks for every ones input.
 
Top Bottom