I recently added one of these to my stable of hollowers. Bought only the head as I need a more substantial bar and handle, my apologies Mr Sorby. I had a spare on hand as well that needed a little modification to accept the Ultima.
The bar is 20mm hard chromed high tensile 4140 steel and the head has a 13mm shaft/pin that fits into the main shaft with 2 m6 grub screws.
Ok this rig is fairly stiff as I'm hollowing some long vases out of hardwood with narrow opening with little or no opportunity to insert a tool rest for support. Also, the grain structure is prone to bad tear out as an attractive swirling about, lousy for hollowing at the bottom of a vase.