These two round holes help the plug stay more securely in place. Inside a standard electrical outlet, there is usually a raised part that fits perfectly into these holes, ensuring the prongs of the plug make better contact with the metal strips inside the socket.

Securing the plug helps maintain stable contact with the power source. These round holes also prevent children from tampering with the outlet and being exposed to danger. Many round-pronged plugs don't fit snugly in outlets, leaving part of the prong exposed, which can pose a risk to small children. Therefore, it is recommended to use flat-pronged plugs with holes if you have young children.

Manufacturers also use the two holes in the prongs to attach seals, helping consumers differentiate between new and used products.

Additionally, while small, these two round holes allow manufacturers to save a significant amount of steel, especially in mass production processes.