These are neat film holders with durable construction and two cool features: they've got removable number wheels to discreetly identify your shots for educational purposes, and there is a button lock to prohibit the darkslide from being accidentally removed unless the holder is inserted into the camera.
Note: Not recomeded for use with Linhof Cameras.
Number wheels can mark film with any number from 00 to 99
Button lock prevents accidentally withdrawing the darkslide