Montbell Lock-On Sandals - IvoryA Montbell creation, the unisex Lock On sandal is a thoughtfully designed piece of footwear. The S shape strap allows you to wear socks if you so wish, whilst also being light and providing all day comfort. The Lock On design has an additional hook and loop back strap which helps secure it in place. Essentially a better, cooler version of a flip flop. XS = UK 3 4 (EU 35. 5 37) S = UK 4. 5 5. 5 (EU 37. 5 38. 5) M = UK 6 7 (EU 39 41) L = UK 8 9 (EU 42