The Knuckle Butt gives you the perfect combination of tank protection, shoulder grip and unique style. Constructed of anti-tear Elastomer to increase durability and longevity. The Knuckle Butt’s unique design lets you quickly check the hydro date of your bottle and get your tank approved in seconds, without having to remove the Knuckle Butt. Just roll it back for inspection. Increase your precision and performance in style.