Attaches permanently to a round handlebar, other bar type, or triple clamp stem nut, so you only need to fit it once. After that, the lock is always available for use, without having to carry or store it. The lock incorporates an integral, pre-coiled, steel cable to go through the face of the helmet or D-ring and back into the lock. If you have the key, you can unbolt the lock from the handlebar. The design makes the bolts that secure the lock to the handlebar/triple clamp inaccessible when the cable is locked, so the locking mechanism not only locks the cable, but also prevents the lock itself from being removed from the bike. Locking your helmet to the centre of your handlebar or triple clamp means that the helmet rests high on the bike, away from dirty/hot exhausts, and usually upright so that rain will not fall into it. The lock has two rubber inserts so that it can be fitted, as standard, to the commonly-sized handlebars or other bars (7/8", 1", and 1-1/4" diameter). Allen/hex key included - no other tools are needed.