Featuring a 2.7 mm wall thickness, the Michelin Heavy-Duty tube is made specifically for those who push their tires in some of the roughest of conditions. Heavy-Duty Tubes are reinforced for off-road applications and provide outstanding protection against punctures and pinch flats. 2.7 mm wall thickness. Features an overlap splice which is stronger than the butt splice used on most tubes. Splice is always placed opposite the valve stem to help balance the tube. Used by those who want the very best. Technical Specifications: Valve stem type: TR-4 (straight metal stem (8 mm diameter)). Tire size: 2.75-21.