Our exclusive Superlok i-fitting tube fittings include the patented red ring gap gauge that make it impossible to over-tighten or under-tighten. When you have tightened your tube fitting nut to the correct depth, the red gap gauge rings pop off, letting you know you have done it correctly, leaving no possibility of error. These tube fittings incorporate a built-in gap gauge for safety and accuracy, allowing you to complete your projects with confidence.