Each of the four inserts in this JessEm Zero Clearance Insert Ring Set has a tiny hole to mark the center for drilling. Simply prebore the insert slightly under the size of your bit then slowly advance the bit upward for an exact zero clearance fit.Designed to be used in JessEm Tool router table insert plates and router liftsEasily change the bit hole diameter with our patented Tab-Loc designPrecision machined from solid 1/4 thick phenolic.No Pre-drilled centerholes.