I bought this headrest for my mesh office chair: https://www.amazon.com/gp/product/B09X45JGCC It is a quality product, except for the “universal mount." The part I designed will let you bolt it on securely to a chair with M6 tapped holes spaced 90mm apart.
Press in two M6 nuts before bolting this to the chair. Then bolt the headrest to the mount. Print with lots (6-8) shells for strength. I printed it in eSUN PLA Pro Black.
Fusion 360 and STEP models included.
The author marked this model as their own original creation.