The Auto Lock-out feature is found on the P645L and P650L models. When the tool magazine has approximately 6 ~ 7 fasteners remaining, the auto lock-out mechanism will activate and lock the primary trigger to prevent empty (dry) firing. This alerts the user to reload more fasteners. But these last remaining fasteners act as a "reserve tank" and can be driven by depressing the Lock-out Override. This allows the user to complete what their doing until re-loading is more convenient. ie. when up on a ladder. This feature is only found in the larger tools because of their primary use for installation work where it's commonly difficult to see if a pin was driven even if there's a hole. ie. ceiling crown installation. Note that the Auto-Lockout feature will lock the trigger by default if 3/8" pins are used. The tools can drive 3/8" pins as long as the Lock-Out Override is depressed.