Micrometer and Case with Magnetic Closure

I printed mine in PETG on my A1 printer sans supports on both pieces. Be careful you don't accidentally print the cover wrong side up by mistake in which case you would need to enable supports.

You will also need a 100 mm long dowel in stainless steel, steel or aluminum. preferably the former and either in 2,5 or 3,0 diameter. The .101 inch diameter dowel holes are currently sized for the 2,5 mm  dowel as a slight press fit. If you want to alternatively use the sturdier 3mm dowel you will need to either (a) alter the design and increase the dowel hole size by that 0,5mm difference or (b) print it as is and resize the holes by that same 0,5 mm after printing. 

You will also need a pair of .250 diameter x .100 inch thick Neodynium pill magnets. When you glue them in place be sure to observe the correct polarity for closure. I recommend taking a pair stuck together and marking the two external facing away surfaces as a guide to installing. It won't be any fun to later discover you accidentally glues them in to repel instead of attracting :-)