The "F" and "S" setting on the Victor M326 Rat Trap is for the sensitivity of the trap. The M326 is for use around machinery or places where the ground may vibrate and accidentally set off the trap. The "S" setting is for a more "sensitive" trigger. The "F" setting is for "Firm", which is what you would want to set it on if it was around machinery or a floor that was sensitive to movement and vibrating.
Answer last updated on: 01/30/2010