What Those Little Holes in Your Plug Prongs Are Actually For

Not all electronic cords look the same. Some have two prongs; others have three or even four. Some have prongs at weird angles, or are even designed for orange electrical outlets. Odds are most people have also seen electrical prongs with holes in them, but the reason for them isn’t common knowledge.

Those two tiny circles often appear near the ends of the metal blades, and newer outlets no longer depend on them. Learn how the feature started, why some manufacturers still use them, what homeowners should know about plug safety, and more.

Why Do Electrical Plug Prongs Have Small Holes in Them?

The holes originally helped keep plugs from slipping out of outlets. Some older outlets had small bumps inside that fit into the holes when someone plugged something in. That changed when Underwriters Laboratories began requiring outlets to hold plugs securely without those bumps.

“Most manufacturers stopped putting the detent nibs on the female contacts, as it made it much harder to meet the maximum force to withdraw and did nothing for the minimum requirement, as the gage had no holes,” according to the National Electrical Manufacturers Association (NEMA).

Basically, the bumps made plugs harder to remove, so manufacturers stopped using them. Today, outlets grip the prongs instead. If a plug starts slipping out, the outlet may need to be replaced. The holes aren’t a child safety feature, either. Tamper-resistant outlets use built-in shutters to keep children from sticking objects inside.

“TRRs work like normal outlets,” according to the Electrical Safety Foundation International. “When you plug into a TRR for the first time, you may be able to feel the internal shutter system engaging. If excessive force is needed to insert a plug into a TRR, there’s a chance that the plug, not the receptacle, is damaged.”

What Are the Holes in Electrical Plug Prongs Used for Today?

Manufacturers sometimes use the holes to hold the metal prongs in place while making plugs. They don’t help electricity flow through the plug, though. The holes can also hold small safety tags or locks on unplugged appliances. However, these shouldn’t replace proper safety equipment. OSHA also has rules for preventing equipment from accidentally starting during certain types of workplace maintenance.

The holes aren’t even required under American electrical plug standards. Manufacturers can make plugs without them, although NEMA has rules for their size and placement when included. They also have nothing to do with grounding. On a three-prong plug, the round prong handles that job. The two flat prongs work the same way whether they have holes or not.

Sources

• National Electrical Manufacturers Association, “Wiring Devices: Frequently Asked Questions” (2023), page 3, “Holes in Blades.“
• Hubbell Wiring Device-Kellems, “Frequently Asked Questions“
• Occupational Safety and Health Administration, “The Control of Hazardous Energy (Lockout/Tagout)“
• Electrical Safety Foundation International, “What Is a Tamper-Resistant Receptacle?“

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