Star Wars "hydrospanner" handheld prop. This uses a length of 1/2" CPVC pipe (the off-white/tan stuff from the hardware store) to unite the files. CPVC is 16mm OD / 12mm ID.

I didn't include a basic cylinder as for most of us, CPVC is easily accessible. If it is not, any cylinder of 16mm OD should work to unify the parts.