Just picked up an APC 48u server rack. There were no pictures of it in the post and I did not notice until I got it home and set up, that the rack rails have threaded holes instead of square cage nut holes. I can’t seem to determine the thread size and pitch, and have a thread gauge coming. Until then, does anyone know anything about this? The people I grabbed it from had used self tapping machine screws and drove them in with an impact wrench. Is this what APC had intended, or is there some $300 proprietary screw I have to buy from them?
Rack screws are pretty standard. You should be able to get a big pack for cheap from the usual online suppliers. Looks like you would want M6x16mm screws.
I have m6 cage nuts from my last rack and they are WAY too big. An M5-0.8 will thread about half way in and then bind, making me think it’s a thread pitch issue?
If they're #10 (US) screws, they'd be 4.8mm major diameter and 24 or 32 threads per inch, so something like M4.8-1.06 or M4.8-0.78. If M5-0.8 thread half way, it sounds more like 10-32.
If you're outside the US, that might be why the previous owners resorted to the ugga-dugga. That will (probably) have wrecked those holes for either their factory pitch or whatever the owners used. You might consider getting a 5MM drill and a 6mm hand tap. You might have fair luck with 10-32 screws, depending on how hard they are to get in your country.
In the US, figured they were a bizarre metric thread someone hammered a sae thread into. #10-24 is sooooo loose though, it’s hard to imagine they would design it with that much slop.