The exhaust adapter for my HF-500 has a small white plastic spacer that holds the head of the screw and allows it to tension the adapter in place. However, the design is bad since there is a 3mm space under the spacer and over the exhaust adapter locating flange. If you tighten the screw a bit too much, the spacer breaks. I've tried to glue it several times, but it kept breaking after awhile.
So, my solution was to design a new one in Solidworks that extends down into the hole in the spindle plate to take up the 3mm gap and better supports the screw head. I then printed it in ABS on my Raise3D N2 printer. Works great, and no more worries about breakage.
Attached is a picture of the new spacer and the STL file I used to print. Enjoy!