Salsa 400+ mm 25+ mm Bicycle Seatposts
About Salsa - "At Salsa, we believe a sense of adventure makes life better. The bicycle can be so much more than just a bike; it's a path to new places, new people, and amazing experiences."
Seatpost length is measured in millimeters. It is typically measured from the bottom of the post to the center of the rail mount.
Offset is often referred to as setback. This is the distance in mm that the clamp is offset from the center of the seatpost.