Spark plug porcelain shards feature little firm points that make it easy for them to identify a breaking point in glass. They can also be used to smash vehicle side windows. Because of their proclivity for shattering glass, spark plug porcelain particles are frequently referred to as ninja rocks.
Aluminum oxide ceramic, which is extremely hard, is used to make spark plugs. The shard’s impact on the glass causes a small structural failure, which quickly spreads the tension across the rest of the screen, leading it to break. Spark plug fragments, while effective, do not always work.
If the spark plug pieces are not sharp enough or thrown with insufficient force, they may not break the glass. Because spark plug porcelain shards have a particular lamination characteristic that reinforces their impact resistance, they are less effective on windshields.
Broken spark plug shards are considered a weapon in several states. This is because robbers have been known to use them to break into cars. Carrying spark plug chips or bits is a crime in the state of California. Individuals found with spark plug chips face a $1,000 fine or a six-month prison sentence.