Hello,
The joint of a Viking cue with the QR pin is .835" though there could be variations that I haven't seen.
I will inquire this morning as to whether all Predator 18 thread shafts come at that diameter.
The Viking QR pin is basically an 18 thread with the top 1/2 of the pin left blank. That top 1/2 of the pin has a dia. of approx. .264" or thereabouts.
All that is required to fit almost any 18 thd. shaft to a Viking QR cue is to open-up the minor dia, of the shaft's insert with a 17/64" drill-bit.
This removes very little mtrl. from the insert but does allow the pin's blank section to enter the hole.
Even with this slight modification, the shaft will still fit a standard/non-QR pin securely.
It would be a good idea to have your friend inform the sales agent at the time of placing the order that this shaft is intended for a Viking QR cue.
Thanx for your inquiry, KJ
OK, a little follow-up.
I spoke with Rick at Seyberts and he measured several 18 thd. Predator shafts for me. They were in the range of .836/.838".
This should fit the Viking cue very well but again, please inform them at the time of placing the order that this shaft is intended for a Viking-QR. They can then modify the insert to insure a proper fit.