For VM, I found Balance pen and pencil set on Mercari. I think I was searching 2 or 3 years.
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The funny thing is, all my other F.C.’s are 0.3.
Shouldn’t ANY 0.5 ring work…?
Have you taken a look inside the TK-matic? There were some posts on Reddit that documented the lead retainer. It is not your typical rubber/silicone nub but an actual ‘clamp’. This eventually gave way to the rubber nub in the Alpha-matics. Or so I recalled.
Here’s the retainer on my own Tk-matic L.
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Yes, I have a couple all-metal mechanism TKs. My Alpha has some plastic in the auto-feed mechanism itself - I don’t recall if the retainer has plastic.
One interesting note about the all-metal mechanism. It can corrode… badly. Not sure if it is a metal-to-metal interaction or humidity or air oxidizing one of the mechanism metals (likely the spring). However, the one I had with corrosion I was able to clean and it is perfectly functional.
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Here is the TK tip clutch, which as @drifand mentioned, is not rubber but a wire pressing against the lead.
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Thanks for sharing these photos. The machining is great, but the precision engineering and design of it really makes me happy. Just the perfect, minuscule force of wire on lead to prevent the lead slipping out but without defeating the ever-so-slightly larger force of the auto-advance piston pushing the lead forward.
How did you remove the lead-retainer mechanism?
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It was already broken when I bought it… unfortunately not disclosed by the seller. It appears to be missing a few pieces like a spring and a cap to hold it all together which is why it looks like it’s sticking up a little.
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This is really fascinating. And a caution… as picking up a TK-matic that’s having trouble gripping the lead isn’t going to be a simple rubber retainer replacement. In all likelihood, not serviceable and requiring a donor pencil (e.g. tragically bad cosmetic condition, but functional mechanism).
How do I pop the clutch mechanism out???
Edit: I tried holding the 4mm pipe while twisting each way. Neither worked 
For some reason it won’t let me load your link. How do I remove the clutch at the nose?
Do you mean this guy? If so, I can say that on my three examples of this mechanism they are all pressure fitted, no threads involved. And pressure fitted is a stretch because on my pristine examples, the piece slides out smoothly without any force.
So how do I force it out?
The 4mm sleeve moves about 2mm inside. Do I simply push it harder??
Can you send a picture?
The mechanism in the picture I sent should be accessible if you unscrew the nose cone from the grip. Pushing the lead sleeve is not part of the disassembly of that part of the mechanism. Typically it will stay with the grip and then slide out of the grip if you point the grip vertically
This was the best I could get focus with :/…
I have yet to find a way to remove it.
Edit: didn’t realize this would look like a gallery for my fingers 
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That part I have never taken out. No idea.
Yeah sorry, didn’t mean to imply you could take the tip apart further. That’s about as far as you can go without breaking it.
I recently learned of this Alteneder set. It was posted on ebay some time back by the seller mikebmw and I found it through a google search.
It has the twist lock drafting pencils AND an item I had not seen before from Alteneder - a slightly diminutive twist lock drafting tip insert with a handle.
If the tip is removed from the handle, it will join the ranks of the smallest MPs/holders.
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I love old drafting sets and tools. What is that metal item in the 3rd picture (above the rulers)?
Micro-rule. Hmm, not sure but it appears to be something similar to a a caliper.
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“Vintage man stuff” - love it! My 47 year old table saw would fit that well. 
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