Tim if I can offer a bit of advice installing these. Assuming your truck has the plastic caps on the bed rails do yourself a favor and pop one off, or at least pull a corner and have a peek before laying these tie downs out. I initially laid out the tie down rail to sit flush with the bed rail - NO GOOD!
The vertical edges of the plastic caps are longer than the actual steel bed lip these tie downs mount to. I had never had a plastic cap off prior to installing these and consequently drilled too high to be able to get a nut on the back side of the countersunk bolts. It sounds like a rookie mistake - and perhaps it was - but once you pop one off for a look you will see what I mean. I messed up the first hole and had to ream it out, even after the fact I had to use a standard SS 1/4" nut over the preferred flanged nuts on 1 or two holes. On The second side I lowered the tie down rail 1/8" and everything lined up well. And yes it's that close...too high and your into the top of the bed rail, too low and there won't be any meat between the bottom of the hole and the bottom of the bed rail.