# what size brass tube?



## dow (Jan 14, 2011)

Does anybody know of a pen tube that the 7mm slimline pen tube would  slip fit into?  I've made several one-piece slims in the past, but was  never really satisfied with the integrity of the nib end of the blank.  I  measured a 7mm tube last night, and the actual outside diameter of it  was .350".  So I guess I'm looking for a tube with an inside diameter of  .352-.353 or so.  I'd be afraid to go smaller than that, as I don't  want the tubes to bind, but if I go much larger, then the parts might  rattle some, not to mention that the blank material would be dangerously  thin on the nib end if the tube was too large.

Thoughts?


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## CaptG (Jan 14, 2011)

Hi Dow,  .350 is the biggest slim line tube I have ever seen.  My slim tubes measure .268 o.d.,  the closest I have on hand that would be a slip fit is an 8mm pencil tube with an i.d. of .280   Hope this helps.


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## dow (Jan 14, 2011)

CaptG said:


> Hi Dow,  .350 is the biggest slim line tube I have ever seen.  My slim tubes measure .268 o.d.,  the closest I have on hand that would be a slip fit is an 8mm pencil tube with an i.d. of .280   Hope this helps.



EGAD!  I measured the wrong tube, I guess.  Thanks for the correction, Cap. Now I feel like a total eejit. I know that 7mm and .284 are the same calibers in rifles.  Why did I forget that when it came to brass tubes?


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## G1Pens (Jan 14, 2011)

I THINK a 7mm tube will fit inside an 8mm tube


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## CaptG (Jan 14, 2011)

EGAD!  I measured the wrong tube, I guess.  Thanks for the correction, Cap. Now I feel like a total eejit. I know that 7mm and .284 are the same calibers in rifles.  Why did I forget that when it came to brass tubes?[/QUOTE]

LOL, I am sure glad I am not the only one who has those moments.


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## soligen (Jan 14, 2011)

Gary,

Another option if you have an archery shop nearby is to take a 7mm tube with you and see if there is an aluminium arrow shaft the right size.  They come in a number of odd diameters.


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## Sylvanite (Jan 14, 2011)

dow said:


> I know that 7mm and .284 are the same calibers in rifles.  Why did I forget that when it came to brass tubes?


Well, measurement nomenclature is different for different applications.  7mm is actually about 0.276 inches, matching neither a 0.268" od brass tube, nor 0.284" diameter bullet.

When we refer to a "7mm tube", we really mean a tube that fits in a 7mm hole with reasonable space for glue.

Rifle caliber names (when they bear any relation to reality at all), typically refer to the diameter that the barrel is bored to before rifiling (the grooves cut into the barrel to make the bullet spin).  In order to form a gas seal when fired, the bullet needs to be the diamter of the rifiling (or a couple of thousandths larger).  Therefore, a 7mm bore, with grooves cut for rifiling, takes a 0.284" diameter bullet.

Welcome to the wild world of misleading measurements.

Regards,
Eric


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## Mac (Jan 14, 2011)

When I first started making bullet pens I would split a piece of a 7mm tube and slide it on a tapered punch and then I would slide the 7mm not sliced in it with glue. Then sand, glue fills the slit and is a good fit.You can see the fit when milling no gap. I then bought some 8mm brass tubes and to me seems a bit slopy to much gap, not centered. So the next bullet pens that I make, I will go back to my orginial way and slice.
You did say 7mm slide into right..


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## wb7whi (Jan 15, 2011)

dow said:
			
		

> Does anybody know of a pen tube that the 7mm slimline pen tube would  slip fit into?  I've made several one-piece slims in the past, but was  never really satisfied with the integrity of the nib end of the blank.  I  measured a 7mm tube last night, and the actual outside diameter of it  was .350".  So I guess I'm looking for a tube with an inside diameter of  .352-.353 or so.  I'd be afraid to go smaller than that, as I don't  want the tubes to bind, but if I go much larger, then the parts might  rattle some, not to mention that the blank material would be dangerously  thin on the nib end if the tube was too large.
> 
> Thoughts?



I use the replacement perfume applicator tubes, woodcraft number 149764

Wayne


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