6311 Bearing

Bore (d) 55 mm

Outside diameter (D) 120 mm

Width (B) 29 mm

Inches (bore × OD × width) 2.1654 × 4.7244 × 1.1417″

Deep-groove ball bearing, medium (6300) series. Seal/shield suffixes (ZZ, 2RS, …) change the closures, never these dimensions — a 6311-ZZ and 6311-2RS are the same size.

What the number means

6 — deep-groove ball bearing
3 — dimension series (medium (6300))
11 — bore code × 5 = 55 mm

Neighboring sizes (medium (6300) series)

Designation	Bore	OD	Width
6309	45 mm	100 mm	25 mm
6310	50 mm	110 mm	27 mm
6311	55 mm	120 mm	29 mm
6312	60 mm	130 mm	31 mm

Same bore, other series

Fits the same 55 mm shaft with a different OD/width envelope and load capacity.

6011 — 55 × 90 × 18 mm (extra light (6000))
6211 — 55 × 100 × 21 mm (light (6200))

Common suffixes on a 6311

Suffix	Meaning
ZZ / 2Z	steel shields both sides (metal, non-contact)
Z	steel shield, one side
2RS	contact rubber seals both sides (SKF 2RS1, NSK DDU, NTN LLU)
RS	contact rubber seal, one side
2RZ	low-friction non-contact seals both sides (NSK VV, NTN LLB)
C3	radial internal clearance greater than Normal (common in motors)
C2	radial internal clearance smaller than Normal
NR	snap ring groove in the outer ring, with snap ring
P6 / P5 / P4	ISO precision classes (≈ ABEC 3 / 5 / 7)

Data provenance. ISO 15, Rolling bearings — Radial bearings — Boundary dimensions (general plan) (ISO). Nominal boundary dimensions per ISO 15; shaft/housing fit tolerances are an application decision — consult a bearing catalog's fit tables. See all data sources.