A holder with size lables for SAKURA Pigma Micron Fineliner Pens. I made it specifically for this set - https://www.amazon.com/Sakura-Pigma-30062-Micron-Blister/dp/B0008G8G8Y/ref=sr_1_5?crid=3SKCZTX58TJMS&keywords=micron+pen&qid=1697867777&sprefix=micron%2Caps%2C106&sr=8-5
The author marked this model as their own original creation.