UCP311 bearing: complete specifications & equivalents
The UCP311 is a JIS B 1559 radial bearing sized 55 x 120 x 66 mm (bore x OD x width) with 2RS sealing. Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 55 mm |
| Outer diameter D | 120 mm |
| Width B | 66 mm |
| Seal / shield | 2RS |
| Basic dynamic load rating C | 79.5 kN |
| Basic static load rating C0 | 45 kN |
| Fatigue load limit Pu | 3.5 kN |
| Mass | 7300 g |
| Housing height H | 80 mm |
| Housing overall length L | 310 mm |
| Mounting bolt center distance J | 236 mm |
| Mounting hole diameter N | 20 mm |
| Manufacturer designation | UCP311 |
| Standard | JIS B 1559 |
| Catalog version | CAT. No. 2203-3/E 2024 |
| Last verified | 2026-09-25 |
Source: catalog reference (CAT. No. 2203-3/E 2024) · extracted 2026-09-25
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (CAT. No. 2203-3/E 2024); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.
Dimensions in inches & UCP-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 2.598 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in UCP-series | 12 mm |
| Largest outer diameter in UCP-series | 300 mm |
| Width range across UCP-series | 31–145 mm |
| Bore position in UCP-series (smallest first) | 11 of 25 |
| Bore above smallest UCP-series size | 43 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| UCP311 | ISO 15 | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | ISO 15 boundary-dimension envelope; seal suffix convention varies by brand (2RS / DDU / LLU / 2RSR) — verify seal design and temperature range. Brand-specific OEM equivalents pending multi-source data. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the UCP311 model number is decoded
NTN ships the UCP311 as a matched assembly — UC311D1 insert swaged into the P311 cast-iron pillow block — so the fitter never has to set bearing-to-housing clearance. Reading the designation: UC marks the wide-inner-ring, setscrew-locking insert; P marks the upright pillow block housing; the 3 code identifies the duty series and the final two digits encode the 55 mm bore. Key mounting figures: centre height H = 80 mm, overall base length L = 310 mm, bolt-hole spacing J = 236 mm, and each of the two feet takes a 20 mm (M16) fastener for the 55 mm shaft. The 3-series section is the heavy-duty end of the range: a UC3 high-capacity insert in the longest, strongest housing, specified for shock loads and long conveyor centres. The upright base carries the shaft parallel to and above the mounting surface, which is the arrangement fan, conveyor and transmission drives use whenever a plinth or rail is available. At 55–90 mm bore the units carry serious conveyor, fan and crusher-feed drives; housing stiffness, foundation condition and bolt torque matter as much as the insert rating. Sawmill and woodworking machinery mounts this unit on saw arbors and feed rolls, where vibration is continuous and the setscrews must be re-checked after the first hours of running. After the first 24–48 running hours, re-torque both setscrews and the foundation bolts — seating of the inner ring on the shaft and crush of any paint under the feet otherwise leaves the bearing loose at the worst possible time. Basic ratings of the UC311D1 insert are 79.5 kN dynamic and 45 kN static; the assembled UCP311 weighs about 7.3 kg.
Typical equipment & failure modes
Common applications
- sawmill arbors and feed rolls
- cement and clinker handling
- sugar-mill and fertiliser plant drives
- fan drives where belt tension, not transmitted torque, sets the radial load
Known failure patterns
- cracked cast ear from mounting on an uneven face and pulling one bolt fully first
- housing-foot cracking beside an over-torqued or under-supported foundation bolt
- grease starvation on long intervals in hot positions, with the ball set running on dried thickener
Selection pitfalls — read before you substitute
- At 55 mm bore the 310 mm base of UCP311 is a structural member: grout or machine the foundation, because a bedded-on-edges housing concentrates the full belt pull on two cast feet.
- The 3-series insert makes UCP311 the highest-rated unit at 55 mm; its advantage disappears on a soft foundation, so spend the saved margin on base stiffness rather than skipping shims.
- As a pillow block, UCP311 needs a prepared horizontal surface at the 80 mm centre height: shim both feet with full-width packs so the 310 mm base seats over its full area.
- The lip seals and slingers on UCP311 suit ordinary industrial dust; submerged or heavy slurry service needs a different sealed arrangement regardless of the load rating.
- Never weld a bracket to the P311 housing of UCP311: local heat cracks cast iron and distorts the spherical bore that the insert depends on.
Frequently asked questions
Does UCP311 interchange with other brands at the same size?
Mounted units of this class follow JIS B 1559 housing and JIS B 1558 insert dimensions, so the shaft size, centre height and 236 mm bolt centres of UCP311 interchange with other makers' equivalent designation. Always re-verify ratings and seal execution rather than assuming the suffix letters match.
What are the dimensions of an UCP311 mounted bearing?
UCP311 takes a 55 mm shaft (insert UC311D1, 120 mm OD) and has a unit mass of about 7.3 kg. Housing figures: centre height H 80 mm, length L 310 mm, bolt centres J 236 mm, foot holes 20 mm for M16 bolts.
What does the UCP311 designation mean?
UC identifies the wide-inner-ring, setscrew-locking ball bearing insert; P the upright pillow block housing; 3 is the duty series; the last digits encode the 55 mm bore. UCP311 is built from housing P311 plus insert UC311D1 (D1 = greasable).
How is UCP311 locked to the shaft, and how tight should the setscrews be?
The UC311D1 insert uses two collar setscrews on the 55 mm shaft. Tighten them to NTN's torque table for this bore size in sequence — half torque on the first, full on the second, then back to the first — and re-torque after the first 24–48 running hours once the collar has seated.
When should I choose a pillow block like UCP311 instead of a flanged unit?
Choose the UCP311 pillow block when the shaft runs parallel to a horizontal base plate, rail or plinth — the upright housing holds the shaft centre 80 mm above the 310 mm bolt-down base. Choose a UCFL flange when the shaft meets a vertical frame face and the housing bolts flat against it.
Reviewed & verified by the MPN Base engineering desk against source catalog CAT. No. 2203-3/E 2024 on 2026-09-25. Read our editorial & correction policy.