Have you ever noticed that flat electrical plugs often have two small round holes on their metal prongs and wondered why?
Every detail in a household product—especially something as essential as an electrical plug—is designed with careful thought to improve convenience, safety, and efficiency for users.

The Primary Purpose: A More Secure Connection

The first and most important purpose of the two small holes is to make the plug fit more securely into the socket. Inside most standard outlets, there are small raised bumps or catches designed to fit perfectly into these holes.
When the prongs slide in, the bumps “lock” into the holes, ensuring that the plug stays firmly in place and doesn’t slip out easily. This design helps maintain a stable electrical connection, reducing the risk of flickering power or short interruptions when the plug is moved slightly.

Added Safety Benefits

These holes are also about safety. By allowing a more stable fit, they minimize the chance of exposed metal when the plug is partially inserted—an especially important feature in households with children. Some modern outlets also include safety shutters or mechanisms that engage with the holes, preventing children from inserting fingers or metal objects and getting an electric shock.

Without these holes, plugs can become loose or wobbly over time, creating small gaps where electrical arcing might occur—tiny sparks that can be dangerous if flammable materials are nearby.

From Early Design to Modern Perfection

In the early days of electrical plug design, manufacturers used small indentations instead of holes. These indentations helped hold the plug in place but caused increased friction when inserting or removing the plug, sometimes producing small electric arcs or sparks.
Over time, engineers replaced the indentations with clean round holes, which not only improved safety but also made plugging and unplugging smoother. The idea was originally introduced by Harvey Hubbell Jr., an American inventor credited with many innovations in plug design. His early models evolved into the standard Type A and Type B plugs that are still in use today.

Efficiency and Manufacturing Advantages

Another clever aspect: adding holes helps manufacturers save a small but significant amount of metal. While it may seem like a tiny reduction, when you produce millions of plugs, even a slight material saving translates into substantial cost and resource efficiency.
Additionally, many manufacturers use the holes to attach security seals or labels—a way to ensure product authenticity and prevent counterfeiting in the market.

Global Standards and Variations

Today, the Type A plug (two flat blades) and Type B plug (two flat blades and a round grounding pin) are common in countries like the United States, Canada, and Japan. These designs follow the NEMA (National Electrical Manufacturers Association) standards.

In contrast, many European and Asian countries use round-pin plugs, which fit snugly into matching round sockets. Because of their natural grip and contact pressure, these plugs don’t need extra holes—the circular shape already ensures a strong, stable connection.

More Than Just Two Small Holes

So, those tiny holes on your flat plug aren’t just random details—they represent a century of thoughtful engineering. They help your plug stay secure, improve electrical contact, enhance safety, reduce manufacturing costs, and even assist with product verification.

The next time you plug in your charger or appliance, take a second look at those little holes. Behind them lies a smart and simple piece of design that makes everyday life a bit safer and more efficient.