The interchangeable insert for standard plates features a 1/2'' opening. The 4'' OD allows this insert to fit into a standard plate with a 3-1/4'' opening. Fits The Following Rockler Router Table Plates:Rockler Router Plate AMakita 1100Milwaukee 5615-5624DeWalt 616-618Bosch 1617- 161Rigid 2930 Combo KitHitachi M12VC (Fixed & Kit)Bosch MRC23EVSKPorter Cable 690Porter Cable 890Porter Cable 7529Porter Cable 97529Porter Cable 8529Rockler Router Plate BDeWalt DW621DeWalt DW621KCraftsman StandardFreud FT 1700EFreud 1702 VCEK