Xacto knife cover
by Thingiverse
I lost the cover for my Xacto knife so of course I modeled and printed a new one. My first real model and probably a bit of overkill, but I had some issues when I tried slimming the profile down. Also, I found that I had to print with a very sturdy raft otherwise it would break free. This fits my Gripster Xacto knife, but I think it will work on the regular metal ones too.
This is a slight revision from the original upload -- it's a bit narrower so the cap should grip the handle higher and not allow the blade to touch.