Needle file grip/handle

Should work OK with the cheapest needle file set you can find at Harbor Freight, AKA:

https://www.harborfreight.com/12-piece-needle-file-set-468.html

Or any file that is 3mm in diameter.

Word from the wise: Take a 7/64" drill bit and drill it out a little so itll fit easier, but still tight.
You could also use a 1/8" bit - SLOWLY - and use some super glue to keep your file inside the handle, but I like the 7/64" method better, personally.

Print vertically, flat part of handle on the print bed.

I used an Ender 3 Pro with a PEI coated magnetic spring steel bed and these turned out fantastic.