| 摘要 |
The present invention reduces the likelihood of damage to an insulator. This insulator for a spark plug is cylindrical and has a through hole that extends in the direction of an axis; is composed primarily of alumina; and at least partially includes mullite. The mullite is included only on an inner peripheral surface side of the cylindrical insulator, and is included in the insulator on at least a part of the inner peripheral surface at a distal end side beyond a portion where the outer diameter is greatest. |
