The Birkenstocks should provide a cross strap over the top of the foot, and be positioned at the big toe joint. This belt provides support for the toes so that they are stable when moving.
The sole should be 22 mm or a little more thick at the heel and toe, and there should be a slight rise above the heel and toe of the Birkenstocks
The front support belt should be smaller than 70 mm or three-quarters of a centimeter
The distance between the leather and the belt is 3 mm, meaning the belt is not tightly fastened