Chevrolet 2009 Silverado 1500 Crew Cab Owner's Manual page 16

Clamp
Installation
1. Position three outer clamps (A), on each side rail.
The positions on the siderails are marked CLAMP.
2-8
2. Position the grooves of
the clamps on the side
rails (A) using the
center groove (B).
3. If the pickup box
has molded bed rail
protectors (A), remove
the insert (C) from
the outer groove on the
clamp, and position
the clamp on the side
rail (B) using the
outer groove (D).