Finally got my Titan rigged with it's PowerGrip Jaws. All from New Zealand... at least that's what it says on 'em.
The ideal size of tenon for the PowerGrips is 114mm. That let's 'em amost close to a complete circle. It'll take a tenon 41mm long.
Pic 1. Jaws closed.
Pic 2. It opens up to accept about 125mm.
Pic 3. Size comparison... sitting beside a SuperNova2. (The #1 jaw on my SN2 is blackened so I can mark the piece without searching for the end of the jaw slide.)