So after testing the 4 inch works best but the flow was wrong so the new ones I miss labeled as 4 inch are really 3 inch and should have great flow to blow dust and other material from bit The upward flow would probobly work fine for wood but with Poly board is sucks the plastic up into the bit and it gets stuck so the downward would be best All center holes are 1/4 inch 2 and 3 inch total diameter in size. The two with set screw holes are 1/4" 20

These have not been tested yet so

Wanted these for work and couldn't really find anything on here for them. Like I said I have not printed or tested these yet so hopefully they work. I also dont know how well they will work or if the 2 or 3 inch will work better. I will update when tested