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Steel Spot And Plug Weld Nugget Size: UPDATE

Did you know that some OEMs specify nugget size for spot welds and steel plug welds? This information is typically found within vehicle-specific repair procedures or can be found under general welding guidelines.

The I-CAR RTS team has been researching OEM body and service repair manuals to provide the most up-to-date information on nugget size for spot welds when squeeze-type resistance spot welding (STRSW) and plug welds when GMA welding. In addition, information on plug weld hole diameter will also be provided when available.

The "weld nugget" the OEM typically provides specs for is the nugget that you see after welding on the vehicle. What can get confusing is that the term "weld nugget" is used for the weld nugget you see before destructive testing and the fused metal you see after destructive testing.

Why does this matter? Because the measurements can be different. When you look at a spot weld, the weld nugget is pretty much what you see and is closely related to the fused metal. However, when you look at a plug weld, the outside diameter of the weld nugget is larger than the actual fused metal. This means that the weld nugget that we are discussing is larger than the fused weld nugget metal that you get after a destructive test.

Located within each of the OEM-specific articles is a Spot Welding, a Spot Welding Requirement/Recommendation and a Plug Welding area. Beneath each area, general information will be provided on what is available from the OEM. It is also indicated if a spot weld and/or plug weld nugget size is available.

General Motors (GM)

If the OEM requires/recommends the use of spot welds, a spot welder will be a necessary piece of equipment for the collision repair facility.

If no OEM nugget size guidelines are available, below are some general recommendations to follow. A destructive test of your test weld will confirm proper weld strength and nugget size.

General STRSW Steel Spot Weld Nugget Size

The size of the nugget will vary depending on the thickness of the metal. A general recommendation for a minimum nugget size is five times the thickness of one metal workpiece. For example, when spot welding two 1 mm pieces, the nugget should have a diameter of at least 5 mm.

General Steel GMA Plug Weld Nugget Size

The plug weld should have a bead height of no more than 3 millimeters or 1/8 inch. To determine the total weld diameter:

  • 6 mm hole = 8-10 mm
  • 8 mm hole = 10-13 mm

General Steel GMA Plug Weld Hole Size

Vehicle makers may have recommendations for plug weld hole size and location. If they do not, holes should be 8 millimeters or 5/16 inch if the flange width will support it.

Follow OEM welding requirements, including what nugget size is required, to help ensure a complete, safe, and quality repair. Please reference the Always Follow Vehicle Maker Procedures article for an explanation on what to use when. If an OEM has unique recommendations, we have provided them for you in the OEM-specific article linked above.

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