Special tips are stocked that cut down on the core size.  These tips fit the standard heads for ¾" tips; but    cut 7/8" or 1" wide.  This reduction of the core is  critical in material that will not yield a tight chip.  They are also helpful in small diameter holes, such as 1-3/4", where the core causes problems by twisting into a birds nest, resulting in blockage of  the chip flow.