This is cut out for a 180mm glass on a 220mm round bed. Glass holder. I have a 220mm round heat bed, but I have only a 180mm round glass, so I needed a way to hold the glass centered and it was too far away to use the binder clip technique - So I made a little brace. This is cut out for a 180mm glass on a 220mm round bed. i have 6 holes drilled in mine, 3 for mounting and the other 3 are open, so I put this in with a 10mm bolt - works great. I found that the 25mm size was a little tight, so I made the 20mm sized one. you can use a combination of these to make it fit on your round bed. Hope it helps someone