SummarySometimes filament would unspool over the side of the spool during prints. On longer prints this would cause print failures as the filament would eventually tighten around the arm of the spool holder. This filament guide slides on the front the of printrbot's aluminum handle and hold the filament roughly in the center of the spool as the filament is pulled off. The dimensions are pretty tight to the handles dimensions to ensure a snug fit. You may need to file/carve a small amount for the initial fitting. You can access the model via OnShape.com here: http://tinyurl.com/jtkyzgePrint SettingsPrinter Brand: PrintrbotPrinter: Simple BlackRafts: NoSupports: NoInfill: 15%