From what I can tell, every pickup truck has four holes stamped on the top of the sides of the bed. They are an odd size - at least mine are: 1 1/2 by 2 by about 5" deep. Too small for a regular 2x4.
I have to assume that there is a specific purpose for them. Campers, maybe?
I used to have a '79 chevy that I built racks into out of 2x4s. I cut them down so they were the size of the holes, and then screwed 2x4s horozontally onto them. It was quite useful when I used to haul firewood.
Also, a lot of newer pickups have better tiedown anchors, but those holes also have holes perpendicular to them that can be used to slip a hook through.
Camper shells, at least, just clamp to the rim of the bed, IIRC.
They are for bed side extenders. You can drop a 1 X 2 into each slot and extend the carrying capacity of your truck bed upwards quite a ways. Some companies sell complete panels that just drop in.
This is primarily for agricultural use. Put some higher sides on the pickup, and you can haul a lot more cabbage.
They’re called stake pockets.
I’ve always called them stake holes. Since I never used them for that, I bought these little things to convert the stake holes to tie-down points: http://www.cargogear.com/catimages/hideahookCAT.jpg They pop up when you need them, sit flush when you don’t.
They are for whatever you can dream up. I’ve seen them used to extend the sides up for carrying hay or other light, bulky item. I’ve seen them used to anchor a couch. I’ve seen small toolboxes hanging from them. Bed toolboxes also sometimes have posts for them.
Me and my dad fabricated a chemical sprayer arm that sits in them, for spraying ditches, fencelines, and other small areas. We also made a seat hanging on the outside for use with a hand held spray nozzle for the same purpose.
I think they were originally intended for side rails and bed boxes, though new boxes just use clamps. They are still there just because people who actually use trucks can usually find a use for them, even if its something as simple as storing a handy tool.
But why such an odd size? For me, the obvious size would be that of a 2x4 (1 1/2 x 3 1/2).
There’s no standard anything that fits in the hole as it is. Even the 1 1/2 dimension is just slightly too small for a dimensioned 2 by anything.
