After adding insulation and glass to my print bed I found I had taken at least a half inch of my z axis out of commission! These extenders bump the threaded rods about a inch up, extending the axis back to normal. I think this may only work if your print bed is higher than the usual. You will have to drill out the holes to your desired size.I used m3 bolts, but the holes will have to be drilled, so anything you have laying around will work as long as you have the right bit.