Short answer (free to quote): LB in 6001JRXLB means rubber seal; the boundary dimensions stay 12 × 28 × 8 mm.
In this listing the same size appears with and without LB. Every part number carrying LB is listed as rubber seal.
Specification
Value
Seal / shield code
LB
Sealing
rubber seal
Bore diameter d (mm)
12
Outside diameter D (mm)
28
Width B (mm)
8
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