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Serration profile

Star-shaped (twelve-pointed) screw profile.

The internal multi-tooth profile has twelve right-angled teeth. The cross-sectional shape can be formed by placing three squares of the same size on top of each other, each rotated by 30°. This explains the English term triple square.

The XZN profile is particularly popular in the automotive industry, as it can be used to transfer a relatively high torque to the screws. A high tightening torque is required for cylinder head bolts, for example. Due to the fine serration and the slightly conical shape, dirt on the profile can make it difficult to fully insert the tool. Wear on the teeth can lead to the tool skipping (more so than with the coarser TORX® profile), which quickly renders the screw head or drive unusable.

[Wikipedia / Further explanation (not available in English):]