We apologize for the confusion. While the title and description correctly listed it as a lightweight keymod rail, the itemized description was incorrect. The itemized description has been changed - thank you for bringing it to our attention.
It sounds like 2.5 mm is correct.
Please be advised that removing the rail does affect your warranty. Because of the design, that rail does not require a lot of torque on the allen screws, so it is very easy to damage the threads. In addition, there are two headless allen screws; one that holds the rail on the barrel nut, and one that assists in removing the clamping tension on the pinching screws at the base. Remove this screw before reassembly - it can keep the pinch screws from tightening.