Abstract: An improvement for a valve of a type having a stem assembly, a rigid bonnet, and a valve base comprised of a lock cavity formed in the bonnet and adapted to receive a lock mechanism therein, the lock mechanism including a locking pin that is positionable between a locked position and an unlocked position. At least one notch or aperture is formed in the stem assembly and is adapted to receive the locking pin of the lock mechanism when in the locked position. In one embodiment, a bonnet sleeve projects away from the lock cavity and is adapted to receive a locking clasp used with auxiliary padlocks. In another embodiment, the improvement is added to an existing valve as a retrofit product by replacing or modifying the bonnet and stem assembly. In another embodiment, the improvement is built into the valve during manufacturing and delivered as a complete solution.