The Tall Skinny Aluminum Windsurfing Extension with the US base cup is an excellent windsurfing mast mast extension. The Tall Skinny's custom alloy and bell shaped tubing provide the best weight to strength available in aluminum. All bases come with a pin and collar adjustment system and the proven US Power-Haul pulley and cleat system. 2 cm adjustment increments. Adds a maximum of 38cm to mast length.