Mitsubishi released three different base models of these “executive sharps” (but only two are pictured here). Each model came in at least two different axis sizes, but one—which isn’t pictured—came in three different sizes (similar to the classic Pentel 5).
In the image above (larger version here), the first row of vertically oriented pencils (from the bottom) includes the three basic types of Mitsubishi executive sharps. I use the ring joint to distinguish between them (from left to right):
Stepped ring joint — MX-50 (grip has a slightly smaller diameter than barrel)
No ring joint — MX-56 (just a seamless join between the plastic grip and aluminum barrel)
1:1 ring joint — MX-57 (where grip and barrel have the same diameter)
Before we dive in, I must note that Mitsubishi model numbers are absolutely maddening—why the heck isn’t the stepped model referred to as MX-55? Likely because the MX-55 already existed around this time (3rd and 4th from left in the same row as the executive sharps under consideration here).
Also worth noting: I don’t have total clarity on the MX-50 model number being used for the stepped ring joint pencils. I’ve seen it numerous times in auction and flea market listings, but I don’t own any specimens with price tags that make this distinction absolutely clear.
As far as I know, the MX-56 and MX-57 were only offered in two axis sizes—short and long—and Mitsubishi used “mini” after the model number to distinguish the short axis versions. For example, the red-gripped pencil in the OP is an M5-56 Mini.
I don’t think the all-black models were particularly special; instead, I think Mitsubishi was simply in the habit of producing black + black variants for each of these three types of pencils (as well as others from this era).
Here are all of OP’s pencils from top to bottom:
- M5-57 mini
- M5-56 mini
- M5-57 mini
Interestingly, I have the same turquoise M5-57 mini, but mine has the cartoon guy price tag at ¥500. None of my Mitsubishi executive sharp specimens has the style of price tag seen on OP’s turquoise mini, and all of mine were priced at ¥500.
Finally, I’m not certain, but I think the stepped model was produced first. It’s the only one I know came in three different axis sizes, which was popular in the early 1970s and fits the time period when these would have been produced.
There’s also a relatively clear cost + luxuriousness progression here:
- M5-50 would have been most expensive to produce, and I suspect Mitsubishi felt a lot of pressure to compete with Pentel when they first introduced these sharps
- M5-56 would have been the cheapest to produce, but the lack of a ring joint really affects the perception of quality (at least for me)
- M5-57 would have been a nice compromise of cheaper production while achieving a sophisticated aesthetic
As my parting shot, I want to mention I’ve got a Mitsubishi W-knock that has an M5-57 price sticker on the clip. I’m kinda hopeful that someone simply put this on there in an attempt to fetch a higher price at auction, but if Mitsubishi re-used these model numbers…that would be a real pain
Anyway, these Mitsubishi executive sharps really stand out in any collection. I love the chevrons on the clip!