Split washers have been experimentally proven to be ine […]
Split washers have been experimentally proven to be ineffective locking devices and can even aid self loosening over time. And yet I see these things in use everywhere, so what gives?
In theory split washers (aka lock washers or helical spring washers) are supposed to work by squishing flat between the nut and the mounting surface when you tighten them. At this point the sharp edges of the washer are supposed to dig into the nut and mounting surface to prevent counter-clockwise rotation.
In practice a lock washer is unable to gain any purchase and does not actually prevent rotation. The only time a split washer might prove useful would be for fastening onto soft easily deformed surfaces such as wood.
The evidence against split washers started stacking up in the 1960’s when a gentleman named Gerhard Junker published some of his lab experiments. He invented a machine specifically for testing the effect of vibrations on threaded fasteners. The first thing he discovered was that transverse vibration loads generate a much greater loosening effect than do axial vibrations.
In general, clip nuts are somewhat easier to install without tools. The lightweight types slide on pretty easily, but I've seen them shift under the weight of heavy gear so that the bolt rests on the bottom of the cabinet's square hole. The heavyweight types might be the best for heavy kit, since the actual nut is held in place within the square hole of the rack rail by the spring and the tension of the bolt itself in the hole.
The problem with the heavyweight clip nuts is that it's damned near impossible to remove one without destroying it. You have to push the nut back out through the rail's hole, slide a knife under the little tab on the front side that holds it in place, and then slide it off. Since the lab is a dynamic place, I might need to install some tool-less rails in a slot where I last used hex nuts.