The inserts and the handle are a friction fit. Do a test print with the handle and one insert first and update print settings if necessary.
I've included Fusion files for both the metric and imperial designs. Download and open your preferred file and update the InsertRadius at Modify > Change Parameters
You may need to download and install the Stencilia-A font from here
The storage STLs account for handle storage also. So if you print the x6 version, you'll have 6 slots for inserts + 1 for the handle
The author marked this model as their own original creation.