Standard TAPRA(R) half face respirator masks come with a central 40-mm NATO gas mask filter thread and exhalation valves on the left and right sides. This is the best configuration for weight distribution, but the central protruding filter can be problematic when you&';re shouldering or handling a firearm, especially in close quarters. With the optional "shooter" configuration, the filter port can be moved to either the left or right side of the mask, and the Low Profile Exhalation Valve Cover (sold separately) installed on the dominant/"cheek weld" side of the TAPR. Please note, all ports on the TAPR Half Face Respirator body are interchangeable, and you can re-arrange them on your own without having to purchase additional parts. However, we cannot guarantee that this type of service will be performed correctly, so if you decide to do it on your own, proceed with extreme caution and at your own risk.