print vertically on the flat sufrace, the file is not optimized for overhangs - it's optimized for easy sanding on a 4mm hand drill and assembly with these I used petg with 3 perimeters for sturdiness. 

 [https://www.ebay.com/itm/265006483654](https://www.ebay.com/itm/265006483654)  (non-affilated)

I bought mine in OBI, 15 PLN for the set (around 3,2€)

1. print
2. insert a 4mm drillbit like you would a corkscrew to a wine cork
3. put the drillbit in an electric drill
4. sandeasly in clockwise direction drill motion (unless your drill is backwards and drills the wrong way) - direction to make sure the sanding does not get the handle off
5. as file is not optimized for overhangs (at least in petg)  I started with wet 60grit, then 120=>200=>600=> 1200, all wet paper to make sure i dont friction melt-it, for really fast sanding I found that a little amount of runnning water allows to get sanding time of one piece get below 2-3 mins for total sanding.
6. drill the hole properly to 4 mm now, same drill.
7. cover handle with acrylic clear spray coat for shiny finish
8. disassemble the files (vice+pliers are sufficient, these are not glued or co-moulded)
9. put a drop or 2 of CA glue in the new handle
10. insert the file. 

Seems like al lot of work, but it's actually pretty straightforward.

I add STEP files, should anyone like to change anything.