Glenn Jilek's Page

Glenn,
A 2 1/2" screw used in a 2x (approx 1 1/2" thick) with the jig set at 1 1/2 will extend approx 1 1/8 into the other wood. Set the jig for 1 1/2 thick and experiment with the depth collar until you get the penetration you want. You can also set the jig for 3/4, 1, or 11/4and see what the penetration would be with the 11/2 fine screws that you have. The screw will not emerge from the center of the stringer but that should not be a problem in your application.
Hope that helps. Off to the depot and lowes.
Ken