Thanks to @Catatat for the mountig clip with one hole for the IKEA MITTLED kitchen strip lights. 

Here is the description from https://www.printables.com/model/188545-ikea-mittled-mounting-clip :

"Mounting clip for IKEA Mittled kitchen countertop light.

This Model is containing two stl files. When in doubt, try v2 first.

mittled_clip.stl - made this version for a printer with tendency to overextrude. Worked fine for me, but according to feedback, it's too small for most printers.

mittled_clip_v2.stl - resized version that should work with most printers

mittled_clip.scad will generate the old “loose fit” version (mittled_clip.stl)." -→ only the one hole version is in the *.scad file!

But… I needed it a little stronger and a little higher version, because I had to get over the bumps from the sidewalls of my L-Shaped kitchen cabinets. So I made the 3 hole version and the higher one easy and fast in Bambustudio, just by merging and cutting.