And if the answer is Harris then which model?

By the way I almost never shoot from a bench.  I'll mostly be shooting prone.

I don't recall what the model # is of the one I have, but definately spend the extra $ to get a model that will tilt from side to side, so you can shoot from a surface that is not level.

I have a Harris BR-S (stands for Bench Rest-Swivel) on my 16" target AR with free float tube (uses a regular swivel stud).  It can adjust from 6" to 9", which is enough for a 20 round USGI magazine (prone or bench).  

Most folks I see like the taller model, which has a height of 9" to 13".  I don't know if they use an adapter or not, or if they have some sort of freefloat tube.

The swivel feature is nice because you can adjust for uneven ground (perpendicular to your muzzle) without moving the legs.  

-Zmeja