This set of 4 phenolic inserts is an accessory to both the Rout-R-LiftFX and the Mast-R-LiftFX. Each router plate comes with one 1 1/2” insert ring standard, but this adds 1/4”, 1/2”, 1 3/8”. and 2 1/2” inserts so you can use both larger and smaller router buts but still maintain support near the bit edge and maximum vacuum from the dust collection system. We recommend adding this to your Jessem lift system!