It is made to fit into the existing inlets. The wrench is purposefully designed to spring open and fail before the nut or the threads on the barrel are damaged. It took a bit of engineering working to make that happen right every time so that folks without a torque wrench wouldn't damage the nut or the threads. That is why we ship a wrench with every barrel nut and the explanation of how to use them specifically includes a torque spec. Exceed that torque spec and the wrench fails... To date we've replaced about 2 dozen wrenches for the cost of shipping in 3 years.
The nut fits any Tikka inlet stock including the Tac A1 chassis with the pass through handguard mount that is pretty tightly toleranced to the barrel. It is also entirely possible to swap the barrel using our barrel nut without a barrel vise or any special tools except a GO gage. The wrench allows you to swap it and torque it down. An adjustable wrench has been used in the field but I don't recommend it because I know that one of those can exceed the torque values that we suggest using for these barrels and actions.
@bsekf PVA/I also make shouldered prefits now that do not require a barrel nut, but you will need a barrel vise to torque them on and off the receiver like a regular barrel.