The Large Slip Bushing is used to narrow the cylinder chamber to provide a better vacuum seal. Using a Busing will also increase comfort against the body, rather than using the cylinder alone. Included with and to be used with the PTV Automatic 3000, PTV Automatic 2000, PTV Manual 3000 systems and all Pos-T-Vac Slip Systems. Large Slip Bushing Size: 1.75″