Pen Tube Sizing?

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MrCrumbs

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New here, hoping to learn more about turning pens. Had a question I was hoping I could find the answer to on here. Does anyone know the actual size of the tubing referred to as 8mm used for pencils? I purchased some 8mm brass tubing to try something and it was too large. I measured my 7mm pen tubing and find it is slightly smaller than 7mm, roughly .25mm smaller, so I was wondering if the 8mm brass tubing used for pencils and penmaking is actually slightly smaller as well. Thanks!
 
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Curly

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Welcome to the forum. Yes the tube is smaller. They are "sized" by the hole they are supposed to fit in. I measured one and the diameter is 0.306" / 7.78mm.
 

magpens

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Yes, the so-called "8 mm" brass tubing commonly used in pen-making is indeed undersize.

The actual diameter is 0.303 inch or 7.69 mm

EDIT :- Don't believe the guy above who narrowly got in ahead of me !!!!! :p ;)๐Ÿ˜
 

MrCrumbs

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Yes, the so-called "8 mm" brass tubing commonly used in pen-making is indeed undersize.

The actual diameter is 0.303 inch or 7.69 mm

EDIT :- Don't believe the guy above who narrowly got in ahead of me !!!!! :p ;)๐Ÿ˜
Thank you! I was hoping this was the case. I ordered some "8mm" tube so now I have my fingers crossed haha. This should also mean the inside diameter is smaller than 7mm as well correct?
 

MrCrumbs

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Welcome to the forum. Yes the tube is smaller. They are "sized" by the hole they are supposed to fit in. I measured one and the diameter is 0.306" / 7.78mm.
Do you happen to have the inside diameter as well? This had me confused bad earlier, I'm so used to ordering actual sizes for materials lol!
 

magpens

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Thank you! I was hoping this was the case. I ordered some "8mm" tube so now I have my fingers crossed haha. This should also mean the inside diameter is smaller than 7mm as well correct?
Ummmmmmm ..... YES !!! ๐Ÿ˜ ๐Ÿ˜ ๐Ÿ˜ ๐Ÿ˜ ๐Ÿ˜ ..... smaller than 8 mm ..... actually 7.30 mm is the ID.
 

Curly

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Mal and I differ again...........slightly. About 0.292" / 7.4mm. Using callipers for inside measurements may be a little erroneous especially in smaller sizes, in part because the points are offset from one another in order to pass by and they are more vulnerable to being bent. There is always operator feel to account for too. Hope you understand I'm not going to dig through a bunch of packed boxes for my small hole gauges on this occasion. ;)
 

MrCrumbs

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Mal and I differ again...........slightly. About 0.292" / 7.4mm. Using callipers for inside measurements may be a little erroneous especially in smaller sizes, in part because the points are offset from one another in order to pass by and they are more vulnerable to being bent. There is always operator feel to account for too. Hope you understand I'm not going to dig through a bunch of packed boxes for my small hole gauges on this occasion. ;)
I appreciate the replies though! Now that I know these tubes are always slightly smaller at least I know I'm looking for something else now haha. I'm thinking a 7mm tube may be a tight fit inside 5/16 tube depending on wall thickness.
 

Curly

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So you are aware the tubes sold under the K&S brand sold in model shops are not the same sizes as the ones used in pen kits. They are thicker and won't work in a pen kit unless you rework them.
 

MrCrumbs

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So you are aware the tubes sold under the K&S brand sold in model shops are not the same sizes as the ones used in pen kits. They are thicker and won't work in a pen kit unless you rework them.
I was hoping I could make one work, but no luck. Trying to make 7mm pen tubes fit tight inside a .30 cal rifle casing, I can center it with the usual suggestions I've seen in the past using heat shrink or teflon tape but on the end with the clip its just not as tight of a fit as using a brass tube to adapt the size to keep the clip from spinning around the top half of the pen.
 

Bats

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I saw on a question on PSI that the ID on pencils are different than the pens. You have to order a specific 8mm tube
I'd be curious to hear more details on this (before it sneaks up and bites me in the ass).

I don't have any 8mm pencil kits handy, but I just measured a couple slimline "7mm" tubes (non-PSI, from Exotic Blanks) and the pen & pencil tube IDs were too close to measure a difference (at least on my cheap vernier calipers - I don't have a small enough telescoping gauge to fit inside). The tubes in both kits were in the range of 6.275-6.3mm.

The OD (measured with a mic) varied even within a kit, though - the pencil had one at ~6.74mm and the other at ~6.78mm (while the pen's were both ~6.75mm), so I suppose there's a chance it's a quality control/tolerance issue, rather than a different spec. Or maybe it's just the 8mm kits. Or maybe it's just PSI kits. Or maybe I'm just guessing and have no real clue.

Hrm... although it does occur to me that when I ordered from EB they were selling the generic 10" 8mm tube pack as spares for the 8mm DuraClick pencil (which is a PSI kit), which suggests they're at least meant to be the same... but I didn't think to compare measurements before making up the kit.


-Bats
(probably just guessing. definitely no clue)
 
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