These are stand-alone models that come in outer diameter sizes of 28, 38, 53, and 75.Sizes 28 and 38 have integrated handles and are used mounted directly on the rotation shaft. Sizes 53 and 75 either allow the customer to design their own handle or come in a set with a handle. Both types may have either one or two indicator needles. Select from a large assortment of rotation ratios to meet your specific needs.