The Simon Hope hollowing rig is one of the best rigs available. You can visit the Simon Hope website at: 

https://hopewoodturning.co.uk/jig-s/hollowing-jig/

The rig takes 19mm (3/4”) tools or 16mm, (5/8”) tools with the reducing sleeve included. The main stem is ground stainless steel with bronze phosphor main knuckle. Each other joint has sealed bearings for easy movement. All steel parts are black zinc coated.  Strong robust construction. For lathes from 5” up to 12” centre height.  (up-to 24” dia hollow forms!) 

To watch a video on this system, please click on this youtube link:

https://youtu.be/J0yqLhDha0k