Size guide for Gaston Mercier products - Categories : Chap'7 Gaston MercierMeasure your calf circumference at the strongest point and the height of your leg from the knee crease to the base of the malleolus Chap'soft Gaston MercierMeasure your calf circumference at the strongest point and the height of your leg from the knee crease to the base of the malleolus Étrivières & Fenders Gaston MercierIt’s the size of the rider who will decide the size of your stirrup & fenders Étriers fermés à coque Gaston MercierIt’s your size that will decide the size of your stirrups Ligne d'bride Gaston MercierFor the Halter Bridle and the Simple Bridle, measurements are taken from one commissure to another, passing behind the horse’s ears. Sangles Gaston MercierTake the thoracic perimeter of the horse from the base of the withers and subtract 125.