The drawback of playing with metalic shaft is that you keep on screwing your shafts to the barrel, because it comes loose with every throw. That is when O'Ring comes into play. It prevents your shaft to unscrew from the barrel. It also works great with conversion points.

But those O'rings are not easy to lock in place. Thus the tool sold with them in order to put them on without any problems.

One O'ring tool  and 10 O'rings per set.