It presses inboard along the bar, with spring force, against the outer flange of the grip.  The force is limited to the spring's own strength, so there is no way it will not let you close or open the throttle if you really want to, a safety advantage over the competition.  The other side of the coin is that to generate secure holding force, the right kind of grip material is necessary, and the grip must be secure enough on the throttle sleeve so it doesn't get pushed in by the spring force, which would cancel some of the force and allow slippage.