Since the price is the only distinctive information printed on the body (besides “Sailor” and “Japan”, which I assume are not the model name) I have taken the habit of calling it “800” for lack of a better name.
This small mechanical pencil is available with chevrons on the clip or, as part of Sailor’s Trident line, with a T. It was also sold as the Sheaffer Sentinel with an “S”. The shape is as minimalist as it gets: a cylinder with a cone at one end.
It is also easily found with various brandings/advertisings.
The construction is full metal, with the one exception for my Sheaffer where the part that holds the clutch and connects the body to the nose cone is plastic.
There is another model, slightly longer (13.3 vs 12.5 cm by my approximate measurements) but very similar in appearance except for the lack of markings on the clip.
This model can also be found in golden and various painted versions.
However, the larger model is built completely differently, with plastic internals (a brass ring around the plastic clutch jaws is the only metal part). The eraser cap is also simpler and the eraser is just plugged in the plastic lead tube, without a ridged metal ring.
I assume the larger model is a newer, cheaper version. Despite the differences in construction, both versions are almost indistinguishable in use. Both are available for cheap on Japanese second hand sites and I highly recommend them if you’re looking for a small lightweight pencil to go with a notebook or in a pocket (while not totally safe, the cone is much less poky than a lead sleeve).