I couldnt find corners to hold my 8.5" by 8.5" glass plate onto the heatbed of my Tronxy P802E, so I made my own! Works with glass 2.5mm in thickness or larger. If you don't have a Tronxy and want to know if this will work for you, I have no idea. My Tronxy uses a (roughly) 3.5mm thick heat bed that is 220mm by 220mm. Take that information and use it as you will.
Uses the pre-existing M3 screws and springs, so you don't have to change anything about your setup, just pop these on, print 1 for each corner. Easy peasy. I made the corner just a smidge shorter than the 2.5mm glass so the extruder nozzle cant hit it.
And, of course, make them out of ABS if you're going to be using ABS heatbed temps.
If you need these for SMALLER glass, or for a different size glass plate and bed, let me know and I'll see what I can do.
Doesnt need supports as long as you orient it right, there's nothing really special to this print.
Since it's such a tight fit, and your glass may not be EXACTLY 8.5 by 8.5, some very light sanding may be required on the parts that touch the glass.