A lug nut or wheel nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks (lorries), and other large vehicles using rubber tires.
What is the meaning of "lug" here? According to the Etymology Dictionary, "lug" is "a broad-meaning word used of things that move slowly or with difficulty".
I've read all the meanings listed in Wiktionary, and I can't understand what exactly "lug" means in "lug nut". I want to understand it in order to remember it better.
A picture I found online:
