The insulator retaining ring on the Makerbot plastruder (Mk3 and Mk4) takes a lot of punishment. If it breaks, you can't print. With these instructions, you can make an emergency replacement that'll keep you going until you can buy / print a replacement. NOTE: This isn't a precision part. It's a quick hack to get you printing again. Using this as a permanent part isn't recommended. Your best bet is, once your printer is repaired, immediately print a replacement retainer and one or two spares.Print the attached image (click on the image to the left and use the "Original Image" link). At full size, it should be 1.75"x1.5" (44.5mm x 38mm). Print it onto sticker paper or a label sheet if you've got it. Otherwise, use regular paper and tape or glue it down.Cut a piece of acrylic (roughly 3/16" or 5mm thick) to the size of the rectangle. I used 0.22" acrylic sheet from the local hardware store and it seemed to work fine.Trim the printout to the size of the rectangle and attach it to the piece of acrylic.Drill holes where marked. A hand-held electric drill will do in a pinch but a drill press is better. The small holes are 1/8" or 3mm and the large hole is 5/8" or 16mm.It won't be pretty but it'll work until you can get a proper replacement.