This one reminds me of the first generation of the S55.
Exploded:
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I don’t have any of these pieces. How different are the ribs on the plastic grip compared to Pentel? Looks like it would feel obviously different.
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This is too cool! I have ribbed grips in black and blue, but I’ve never even seen the red variant before!
Mitsubishi and Pilot both have deep—and underrated—executive lineups.
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These have finer fluting (?) than the super OG Pentel 5s—more grooves, less depth—and in my view, the Mitsubishis are more pleasant in the hand.
Also, I’ve only seen these types of grips on short axis pencils (contra Pentel, which has them on full size pencils), so that probably contributes to the feel as well.
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Here’s an auction pic I saved. 0.3 version… so this is the M5-52. Not that ‘far away’ from the ‘chevron clip’ Mx-57 with a similar(?) ring.
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Great find! I know of at least 3…maybe 4…different styles with the fluted plastic grips, but I’ve never seen a model number designation before.
Makes me wonder if the variants of this style are MX-53 or MX-54 
I think I may have 2 or 3 of the lower cost all plastic version. M5-51 maybe? If the logic follows from the M5-56 being the lower grade from the M5-57.
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Ah yes, logic—if only that were a factor here 
I got the blue one a couple of years ago and then finally picked up the black one. I really like these… although a bit on the small side. Some nice little touches all around:
- Fluting on both the grip and main body, in different thicknesses. An interesting contrast.
- A sliding pipe guide.
- All steel construction lead mechanism.
- While the body comes in 2 parts, you don’t need to separate it to extract the mechanism.
- Slight taper to the metal eraser cap (unlike most that are a straight cylinder).
What’s curious about my two compared to the red example in the first post, is that the metal mechanism tube narrows about 10 mm from the spring (both are 0.5 mm). Most metal mechanism tubes are just straight all the way through. I wonder what influenced this design decision… and if it’s a sign of a 2nd release.
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The more complicated the mechanism, the greater the likelihood that it was an earlier generation…
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Yes, I agree for the most part. Sometimes a change ease the cost of manufacture while making a minimal or negligible impact on the product, or it’s necessary to deal with a factor that can cause a problem–making the updated version better to have for long term usability.
Do you know if the colorway set is just blue, red, and black? Or are there any other colors?