Spark plugs are a vital part of any combustion motor, and they’re also one that will wear out in time. While you can technically use a normal deep well socket to remove spent plugs, there’s a good chance you’ll damage good plugs.
Instead, you should always use a spark plug socket when working with these important components. While there are two common spark plug sizes that cover the majority of vehicles, other sizes do exist.
The chart at the bottom should cover almost any spark plug size you encounter whether it be a car, truck, motorcycle, lawnmower or other small engine.
What is a Spark Plug Socket and How does it Work?
Spark plug sockets are designed specifically to handle spark plugs. They have two possible interiors, both of which are designed to carefully hold the plug without damaging it.
Magnetic sockets use magnets to hold the plug, while rubber inset sockets create a soft rubber cradle for the plug to sit in.
While this doesn’t sound like anything special when compared to a deep socket, it really can make a difference. The specialized bed helps prevent slippage during work, which in turn makes installation and removal faster.
For many models of car where spark plugs are seated deep within the engine block, this could mean a whole lot of time saved or busted knuckles. Additionally, there’s far less risk of damaging the insulation when using a spark plug socket.
Spark Plug Socket Sizes
There are only a handful of spark plug sockets available, both as deep and regular. Deeps sockets will work much better when dealing with a recessed plug.
Additionally, most sockets will fit a standard 3/8” drive and kits may even include one or more extensions or swivels. It’s usually best to aim for thin walls, as these can get into deep recesses easier no matter what socket size.
The most common spark plug size is 5/8″ but the actual size you need is very vehicle dependent. Spark plug sockets are usually sold individually (Gearwrench example) but also come in sets. Some include various sizes and extensions, such as this higher end set by Sunex.
Please note that 7/8” sockets are rarely included in socket sets due to their more specialized use and require a 1/2” drive.
While 12-point versions of many sockets are available (sets often include a 12-point for 14mm plugs), the 6-point option tends to be much more common. Only a few vehicles, such as some newer BMW engines, use 12-point plugs.
Spark Plug Socket Sizes Chart
Note: It’s rare that a particular engine manufacturer sticks with a single spark plug size across all its products. The chart simply provides common use applications. It’s recommended to do a Google search for the year, manufacturer, and type of engine you have to get the most accurate results. For example, “2020 Mazda 2.5L spark plug size”.
|Spark Plug Size||Application||Notes|
|14mm||Newer European vehicles, newer Asian vehicles, motorcycles (some)||12pt thin-walled for many BMWs|
|5/8"||Many newer vehicles (GMC, Nissan, Chevy, Subaru), small engines (Briggs & Stratton, Koehler) in lawn mowers or string trimmers||Most common size. 16mm will also work|
|18mm||Motorcyles (most), some small engines|
|3/4"||Older GM vehicles, lawn mowers, chain saws|
|13/16"||Older vehicles (large engines), lawn mowers, string trimmers||2nd most common size.|
|7/8"||Tractors, older vehicles, aviation|