I needed an idler pulley with 20 teeth for a GT2 belt on my delta printer that run on ball bearings. Because I couldn't find an industrial made pulley on the internet that was available quickly, I designed this one that uses two F604 ZZ ball bearings. It can be used with the 6mm GT2 belts commonly used in 3D printers. The height of the assembled pulley is 15.2mm.