Like Mal, i would pe interested in knowing what type of mechanism does it use.
I haven't made that particular kit. The one I make has a click type mechanism that pushes the lead forward a set amount. I would prefer to have a more traditional open clutch that releases the lead until you release the button. Same as the artist/shop sketch pencil.
I get them from one of my China suppliers. They require a special step drill, mandrel and bushings. They are a tubeless design, really simple.
Here is a disassembled pic, The step drill creates a ridge inside the blank and the nib screws on sandwiching the mechanism. No erase on this model however there are 0.5mm pencil kits that have an eraser. Requires a different mandrel and step drill.
Looks a lot like the parts from the Pentel pencil several of us make. Thew Pentels we use have gotten expensive since the first one I made many years ago. Nice job.
Do a good turn daily!
Don