This is a car holder for the Acer Iconia 7" tablet.
It is designed to fit the posts on the headrest in a 2012 Skoda Superb, but I would venture to guess it might fit similar year Volkswagens and Audis. The center to center distance of the posts is 148.2mm.
I've added the SolidWorks assembly file (in pack&go) so people with SW2013 or newer can adapt it to suit their needs. Attached is also a ZIP of the STL files for printing (they are rotated in the orientation I printed them).
This holder will probably be quite easy to adapt to other tablets by changing the length of the 6mm steel pins connecting the hub and hooks. The steel pins are glued into their sockets.
In the assembly I've added an M5 bolt, washer and nut, but I ended up using an M6 for closer fit. (the hole was reamed with a 6mm drill bit). The frame strap clamps the headrest post with 2 small, tapered wood screws.
The holder was Printed in ABS, but could just as easily have been made in PLA. I'll be printing one more with taulman3d.com/ 's 618 vinyl to see if I can improve the strength. All parts were printed with fairly high infill, and, I believe, 3 layer surface thickness.
I have had a couple of breaks in the hub at the roots of the right and left pin holes from overzealous kids feet getting in and out of the car, but they were easily repaired with superglue.
.... and yes! it is completely over-designed/engineered :)