UCP321 bearing: complete specifications & equivalents
The UCP321 is a JIS B 1559 radial bearing sized 105 x 225 x 112 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 | 105 mm |
| Outer diameter D | 225 mm |
| Width B | 112 mm |
| Seal / shield | 2RS |
| Basic dynamic load rating C | 204 kN |
| Basic static load rating C0 | 153 kN |
| Fatigue load limit Pu | 9.35 kN |
| Mass | 35000 g |
| Housing height H | 140 mm |
| Housing overall length L | 490 mm |
| Mounting bolt center distance J | 380 mm |
| Mounting hole diameter N | 36 mm |
| Manufacturer designation | UCP321 |
| 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 | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 4.409 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 60 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) | 21 of 25 |
| Bore above smallest UCP-series size | 93 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| UCP321 | 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 UCP321 model number is decoded
UCP321 belongs to NTN's UCP line of cast-iron pillow blocks built to JIS B 1559 housing boundary dimensions around a JIS B 1558 UC321D1 insert. The code breaks down as insert family UC, housing form P (pillow block), duty series 3, bore code ending in the 105 mm shaft size; the unit is built from insert UC321D1 and housing P321. For layout work on UCP321: the 105 mm shaft centre sits 140 mm above the sole (H), the footprint is 490 mm long (L), bolt centres are 380 mm (J), and the foot holes suit M30 (36 mm) bolts. 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. Units in this bore class live in quarries, steel plants and port equipment: the ratings are high, but dust, water and foundation movement — not fatigue — usually decide the service life. Cement plant clinker conveyors fit this size under insulation and heat shields; radiant heat dictates both the grease grade and a relubrication interval far shorter than the load alone would suggest. If the unit is the locating bearing, clamp the inner ring with both setscrews and keep the housing feet tight; the opposite unit on the shaft must be the float design with slots, or thermal growth preloads both bearings. Basic ratings of the UC321D1 insert are 204 kN dynamic and 153 kN static; the assembled UCP321 weighs about 35.0 kg.
Typical equipment & failure modes
Common applications
- quarry and aggregate screens
- ship-loader and stacker drives
- mining and port conveyor pulleys
- vibrating feeder and screen-adjacent positions where setscrew retorque is routine
Known failure patterns
- setscrew loosening and inner-ring fretting on a shaft that was never re-torqued after run-in
- insert brinelling from hammer mounting or from belt tension applied to a stationary unit
- over-greasing that churns the charge, overheats the bearing and blows the seal lip
Selection pitfalls — read before you substitute
- UCP321 is located on the shaft by setscrews only; for shock reversing drives consider an adapter-lock insert family instead, since setscrew points indent the 105 mm journal over time.
- XL units like UCP321 (105 mm bore, M30 bolts) are grouted, shimmed and aligned as civil works; bolting them straight to bare plate guarantees movement and foot cracking.
- The 3-series insert makes UCP321 the highest-rated unit at 105 mm; its advantage disappears on a soft foundation, so spend the saved margin on base stiffness rather than skipping shims.
- As a pillow block, UCP321 needs a prepared horizontal surface at the 140 mm centre height: shim both feet with full-width packs so the 490 mm base seats over its full area.
Frequently asked questions
How is UCP321 locked to the shaft, and how tight should the setscrews be?
The UC321D1 insert uses two collar setscrews on the 105 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 UCP321 instead of a flanged unit?
Choose the UCP321 pillow block when the shaft runs parallel to a horizontal base plate, rail or plinth — the upright housing holds the shaft centre 140 mm above the 490 mm bolt-down base. Choose a UCFL flange when the shaft meets a vertical frame face and the housing bolts flat against it.
What are the dimensions of an UCP321 mounted bearing?
UCP321 takes a 105 mm shaft (insert UC321D1, 225 mm OD) and has a unit mass of about 35.0 kg. Housing figures: centre height H 140 mm, length L 490 mm, bolt centres J 380 mm, foot holes 36 mm for M30 bolts.
What does the UCP321 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 105 mm bore. UCP321 is built from housing P321 plus insert UC321D1 (D1 = greasable).
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.