The WB-MS10-AA is a WORKBENCH Bench frame with built-in attachment receiver. This will replace the undercarriage frame to upgrade the old WB-MS bench frame to accept current line of attachments. Please note that this upgrade will NOT work with WB-MS systems purchased before 2008. System models compatible with the WB-MS10-AA are those, with the workbench, that have the semicircle adjustment bracket. In addition, if the front linkage tube measures 11” or 11 ½”, it must be replaced with one that measures 9 ½”.