The two primary spark plug sizes that accommodate the majority of vehicles are 5/8 inch and 16mm. These are often interchangeable or considered equivalent for the hex size of the spark plug, which is the part a socket fits onto for installation or removal.
While 5/8 inch (approximately 15.875mm) and 16mm are the most common, spark plugs come in various hex sizes to suit different engine designs and manufacturers. Understanding these sizes is crucial for using the correct socket and performing maintenance effectively.
Common Spark Plug Hex Sizes
Here's a breakdown of common spark plug hex sizes:
| Spark Plug Hex Size | Common Applications & Notes |
|---|---|
| 5/8 inch (16mm) | This size covers the majority of spark plugs across a wide range of vehicles, making it the most frequently encountered. |
| 14mm | Increasingly found in newer European and Asian vehicle models. |
| 9/16 inch | Used in specific applications, notably some Ford vehicles. |
| 13/16 inch | Less common, but still used in some older or specialized applications. |
| 7/8 inch | One of the less common larger hex sizes found in certain applications. |
| 3/4 inch (18mm) | Another less common size, used in a limited number of applications. |
Key Characteristics of Spark Plugs
Beyond their hex size, spark plugs generally share some common design features related to their fitment:
- Most spark plugs feature a 6-sided (hexagonal) top designed to be gripped by a corresponding socket.
- It's worth noting that some specific engines, such as certain BMW models, may use spark plugs with a different number of sides, requiring specialized tools.
Using the correct spark plug socket size is vital to prevent stripping the spark plug's hex or damaging the socket itself. Always ensure a snug fit before applying torque.
