@frankchannel / Corey first posted his design of a mount to hold a drag knife or a pen in the Hallowe’en contest thread but I thought that it deserved a thread of its own. Here are the design files that Corey linked to:
Corey exported the files in both .stl and .obj format. Here they are:
SideMount_DragKnifePen.zip (156.9 KB)
If you go with a drag knife similar to the one that Corey used, here is a link that describes how to install the blades, etc. Note that the video does not show Corey’s mount design. I’ve linked to it to show how the blades are inserted into the holder.