Good idea, but unfortunately it’s a bit too thick. I’m using an OHTO extra fine ink pen, but the sides of the stencil get in the way of using the pen. if you adjust your pen tip to protrude further from your pen body you can at least use the lines and boxes but the letter and numbers will grab the nib of the pen. so you’ll need to either increase the size of the letters and numbers or make it thinner so you have less contact with the ballpoint nib or Maybe an ultrafine drafting pencil instead?