Firmest of all of The Sticks.
The Stiff Stick is for those who love / need deep massages; by pressing lighter, you can simulate a light massage.
It is a favorite of most athletes; if you are up to 5' 10" and flexible, easy to use by yourself on all major muscle groups.
Stiff or firm Sticks can provide deeper pressure and are most appropriate for:
More muscular physiques,
Larger individuals, or
Those that especially enjoy deep pressure.