The part number is 128643, torch mounting sleeve. You can download the Powermax1000 service manual from the Hypertherm | Plasma Cutters | Plasma Cutting Equipment | Metal Cutting Equipment website. Click on the "downloads library" tab, choose your system, choose the service manual. It has good breakdowns with part numbers for every system component, as well as a great troubleshooting section. These manuals are available for most Hypertherm systems for free.
You can also get part numbers even easier by calling Hypertherm tech service, also toll free, and they can easily provide you with part numbers as well as troubleshooting advice. The tech service guys at Hypertherm are a very talented, helpful group.