There is a carbon biscuit with a .26" hole for the original outsert carbon arrows, and an ICS carbon biscuit with a .32" hole for either ICS carbon arrows or 20XX sized aluminium arrows. The aluminium arrow size biscuit has a .36" hole and will take up to a 23XX size aluminium arrow and still have a somewhat loose fit which is the reccomended fit for the arrow. It is easier to tune the rest and the bow with a looser fit between the biscuit and the arrow. The closer the tolerance between the arrow and the rest the more perfect the position of the rest has to be, and the more critical the tiller of the bow in order to get good results with this rest. Good luck hunting!