Round protrusions on side of 18-wheeler trailer

They are the back side of where we can hook straps to hold freight in the truck just like a load lock. Maybe a driver can put a picture in to show you.

 

If your driving next to that truck I would not stay there long. J/K

 

well, on that truck it is a point of reference so the driver knows how much of the trailer he jacked up when he calls in his accident to dispatch.

S.wing W.ide I.t's a F.ull T.railer

 

S ee
W hat
I
F**ked
Today

 

Really, other than the anti Swifty jokes here, it's for load straps. Kinda like the ratchet straps that you would use to hold a motorcycle or junk down on a flatbed. You see, with a trailer like that, you can't place load locks in it because the walls are too thin and flex out and then you have a guy in the trailer swearing up a storm because he just took a load lock to the head. They also make bars that look like load locks, well kinda, that hook into those to keep the load from moving around. They have stopped using this system in new trailers (the bumps) and now have ribs that have the hook spots for straps.

 

Usually you see trailers like that on one lane dirt roads out in the desert 'cause that's where their GPS told them to go...

 

or where their dispatchers told them to go

 

I drive vans around, but never really questioned those things, but they don't look like strap rail mounts from any of the trailers I've ever been in. Generally there are two stamped and formed metal bars at two heights on the walls of the trailer, four total. This is for the driver to strap the load in with some pretty chintzy straps that some nut invented with his own three hands.
Personally, when I've had to deal with thin walled boxes, I've used a combination of those straps and load bars so there is control of the amount of pressure so I don't force the walls out. This method also works good for separating the load or centering a short load in a trailer for weight distribution, it hasen't failed me yet.
I always thought those things were some sort of vent for the walls, you only see them on dry vans. Reefers have foam in the walls, and the venting is done by the refrigeration unit in some modes.