USED This 1 groove sheave measures; 3 1/4" for the outer diameter, 2" for the inner diameter which is measured according to standard pulley measurements. The sheave measures 3/4" thick excluding the hub. The hub itself measures 1/2" inner diameter where the shaft would be located. The groove on the shaft opening is 1/8" by 1/4". The original manufacturer is unknown; however, there is a part number of 3 1/4-B on the part.