How far does each side rail protrude inside from the rail into the bed of the truck?
Only 1 inches on each side. As a truck owner, you have come to realize that the most usable bed space is between the wheel wells (to slide sheets of plywood, sheetrock, luggage, etc.). As these rails only protrude 1 inches on each side, and most wheel wells on the most popular “FleetSide” trucks protrude inside the truck bed anywhere on the average of 6-8 inches on each side. This means that there is very little, if any practical and usable truck space that is lost by the installation of these rails!