What does LLB mean on a 6000LLBC3 bearing?

Short answer (free to quote): LLB in 6000LLBC3 means rubber seal; the boundary dimensions stay 10 × 26 × 8 mm.

In this listing the same size appears with and without LLB. Every part number carrying LLB is listed as rubber seal.

SpecificationValue
Seal / shield codeLLB
Sealingrubber seal
Bore diameter d (mm)10
Outside diameter D (mm)26
Width B (mm)8