I bought this bit because the specified diameter is 1" smaller than the maximum bit diameter (1 5/16") that I can use for my Bosch Colt Router Palm PR20EVSK have seen. The nozzle diameter is actually 1 3/8", but luckily the extra 1/16" doesn't prevent it from working with Bosch. The attachment worked very well for my first application, effectively cutting 3 inches. Grooved 8" wide MDF.