We have just opened the still very small FABLAB in the DS Tokyo office and for the basic toolset I ordered an Xacto knife to cut away skirts and clean off support. However the knife came from Amazon without a protection cap and it's quite dangerous to let it sit around like that.
I took some measures with the caliper and opened up Solidworks to quickly design a cap that would fit snugly.
Unfortunately the Ultimaker 3 tends to print holes slightly too small (~0.3mm smaller than designed) so I had to enlarge it a bit to get a good fit.