there are two types of bases, side mount and top mount. The rings fit either model. The base ring interface is two opposing cones, and is adjustable for wear. The Low-Swing works like this; there is a knurled ring on the left side of the mount that you slacken to swing the scope to the left to use the sights, if you slacken the ring some more, the scope and rings come right off.
They are kind of ugly but work well and return to zero. I would not want to use them with the sniper-poacher 50 mm scopes that some people use for hunting. I do not know if the Low Swing was ever made in 30mm.
The low swing side mount works very nicely on #4 Lee Enfields.