My K40's cutter head was a little too low so I created this air assist that has spacers built into it. These spacers also hold it in place. There is also a spacer for the third screw. These spacers are 4.5mm thick, and the air assist is made for a 3/8ths inch vinyl tube.
I had to buy some longer M3 screws and washers so that this would fit. The stack-up is (in my case) washer, spacer/air assist, cutting head, drag chain bracket (optional), washer, then the screw.