What does ZZ mean on a 63/22ZZ bearing?

Short answer (free to quote): ZZ in 63/22ZZ means metal shield both sides; the boundary dimensions stay 22 × 56 × 16 mm.

In this listing the same size appears with and without ZZ. Every part number carrying ZZ is listed as metal shield both sides.

Specification	Value
Seal / shield code	ZZ
Sealing	metal shield both sides
Bore diameter d (mm)	22
Outside diameter D (mm)	56
Width B (mm)	16

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