One pencil support two lead size. Sailor Cassette Mechanical Pencils if you see the second last photo, the two plastic tube, pink is for 0.5mm, white is for 0.3mm. You can plug any of one into the tip and make it 0.5mm or 0.3mm. I will put the pink 0.5mm into it and leave white 0.3 aside. When you want to replace, push the cap and plug out the tube form the tip and replace.

The entire mechanism is different from the normal pencil. Also it can be twist to open, I don’t recommend people who are not familiar with it to do so. It maybe a bit complicated in its mechanism. There are products around 70s. Pls understand this is a different type of mechanical inside.