White plastic roller/wheel mounted in a steel frame bracket. Total approximate size of assembly is 0.393" (10mm) x 0.945" (24mm) x 0.669" (17mm). Steel frame bracket has a 0.118" (3mm) diameter x 0.748" long (19mm) shaft and two 4-40 size holes for mounting. Contact portion of the roller is 0.433" (11mm) diameter x 0.315" (8mm) wide. Plastic roller can be removed by simply opening up the steel frame. Perfect for small robots!