What is meant by the reach of a spark plug?

What is meant by the reach of a spark plug?

• A. The overall length of the spark plug.
• B. The length of the threads on the spark plug that screw into the cylinder head.
• C. The pitch of the threads.
• D. The diameter of the electrode tip.

Answer: (B)

Reach is the distance the spark plug threads extend into the cylinder head—the length of the threaded portion that screws into the head. This depth determines how far the insulator and electrode sit inside the combustion chamber, which affects spark placement and sealing. The description that matches this is the length of the threads that screw into the cylinder head. If the reach is incorrect, the plug may not seat properly or place the spark gap in the optimal position. The other options describe unrelated dimensions: overall length is the total plug length, thread pitch is the spacing of the threads, and the diameter of the electrode tip does not define how far the plug threads go into the head.

Reach is the distance the spark plug threads extend into the cylinder head—the length of the threaded portion that screws into the head. This depth determines how far the insulator and electrode sit inside the combustion chamber, which affects spark placement and sealing. The description that matches this is the length of the threads that screw into the cylinder head. If the reach is incorrect, the plug may not seat properly or place the spark gap in the optimal position. The other options describe unrelated dimensions: overall length is the total plug length, thread pitch is the spacing of the threads, and the diameter of the electrode tip does not define how far the plug threads go into the head.