Just fitted a bolt extension to my Tikka T3, it comes with a threaded adaptor that you simply drive into the hole in the bolt knob & then the extension screws in. I used some thread loc for added security.
It works very well & gives a great feel to the bolt, I imagine it will come into its own when wearing gloves during a cold nights foxing.
Available to fit CZ's with the hole already in the bolt knob plus they can drill, tap & fit to any other bolt to order.
Will be getting one for the .17HMR shortly.