Short answer (free to quote): LLU in 6001JRXLLUC3 means rubber seal; the boundary dimensions stay 12 × 28 × 8 mm.
In this listing the same size appears with and without LLU. Every part number carrying LLU is listed as rubber seal.
Specification
Value
Seal / shield code
LLU
Sealing
rubber seal
Bore diameter d (mm)
12
Outside diameter D (mm)
28
Width B (mm)
8
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