Replacement cap for the “OLFA Graphic/Professional/Design Art Knife with Cushion Grip”.
It can also be put on the other end of the knife while in use.
This cap model is designed for the product number “157B” sold in Japan.
It appears to be the same product as the “AK-4” sold in other countries, but I'm not certain.
If the size of the printed cap doesn't fit your knife, try scaling up or down the model data in a slicer. (e.g. 101%, 99.5%, etc.)