Why Are There Holes in Electrical Plugs?

Here’s one you see every single day of your life. But did you ever wonder why there are (almost) always holes in electrical plugs prongs? Creatively presented, this bit of everyday practical knowledge just might win you a bar bet.

Let’s solve this with a pop quiz.

Are the holes there to…

A. Save materials to reduce manufacturing costs?

Nope. While all that excess metal could, in theory, be recycled and converted into more plugs, it’s not the answer. Besides, I’ll bet Dunkin Donuts holds a patent on the productive use of what used to be holes. Besides, if this were the case, why not make the holes more oblong to save even more money?

B. The holes are there to catch on a spring-like device inside the plug to make it harder for the plug to slip out of the socket.

Again, nope. But there is just a hint of truth to this one. Back in the early part of the 20th century, there were a couple of patents floating around for plug prongs with notches in them. The interiors of receptacles would be equipped with springlike blades that fit into the “U-shaped” notches. To our eternal disappointment, modern plugs don’t use any of that, and nothing inside the receptacles locks into the plug’s round holes.

C. The holes are for safety locks to prevent people (think kids) from plugging stuff in that shouldn’t be plugged in. Or to “lock” plugs into outlets with some kind of bar inside that goes through the holes.

Nope, but again, with a hint of truth as such locking devices do exist, but the holes were there long before locks came on the market.

D. Because it’s always been that way.

Winner, winner chicken dinner, but with a caveat. The prevailing wisdom is that once upon a time, manufacturers of plug-like stuff used the holes for manufacturing convenience—to hold on to the prongs while the plug body was formed or some such thing. Over time, these holes worked their way into the ANSI standards and are now precisely documented in terms of diameter and placement on the prong. However (and here’s the fun part), there is a footnote saying the holes are completely optional.

So there you have it. Modern electrical gear manufacturers make holes in plugs, possibly for no reason at all other than “it’s always been that way.” If only that kind of persistence applied to the price of bone-in ribeyes.