I bought this attachment to carve dados in 3 tool holders I am making for a rotary spindle duplicator. The handles require a 3/8" slot for attaching cutting tools. I used this attachment to cut 3 slots and the cutting tools didn't fit the slots. I measured the nozzle with a micrometer and found it to be 0.371. ", which is 4 thousand less than it should be .375". The cutter shank is .375"". A small adjustment with a wood rasp solved the problem, but when buying CNC bits I expected them to be the size advertised. I still gave the bat 4 stars. It's very sharp and made a nice clean cut in one pass. If you don't need full accuracy, it's worth it.