I'm too tall for the headrest on my Staples Dexley, it hits my shoulders. This adapter brings the headrest back a bit and up about an inch or something. I'm 6'3" and it's much more usable now. The adapter will require some new hardware, including some longer bolts to attach the adapter to the chair as well as two nuts and two bolts to attach the headrest to the adapter. Hopefully this can be a starting point to help all the tall Dexley users out there.

I printed at 50% infill and it seems pretty sturdy, the chair is flexing more than the adapter.
Test printed on Anet a8