Screw what came with it then. Go buy a plastic screw from HD that IS a normal size that people do have drills and taps for.
Or if you are just trying to like extend two pieces of plexiglass as a hanger then drill two holes and zip tie it. Or get a longer piece of plexi.
There has to be an easy solution to what you are trying to do. Maybe you should explain it a bit more.
PH Probe Holder:
Strip of plexi - heat over stove - bend - drill hole - done.
Although in this case, the bottom piece was glued rather than heated and bent.
Most probes come with a rubber sucker thing to stick to the glass. I just cut the cup off leaving the rubber band and that acts as the "stop" so the probe won't fall all the way through the hole.