Two-Bolt Pillow Block Bearing, 2-1/2 in Bore, Double-Row Spherical Roller, Concentric Collar Lock, Non-Expansion

What this part is:
A Dodge Unisphere II two-bolt pillow block: a one-piece iron housing carrying a double-row spherical roller insert on a 2-1/2 in shaft. It is a heavy-duty replacement for a ball-bearing pillow block of the same footprint, chosen when the load, the shock or the misalignment has outgrown a ball unit.

Decoding the order code:
P2B = pillow block, two-bolt base. UN2 = Unisphere II, Dodge’s concentric-collar spherical roller line. 2 = 2 inches and 08 = 8/16 in, so 208 = 2-1/2 in bore. Dodge’s own item number for this unit is 048008; the global part number is 521485 and the insert alone is BRG-UN2-208. Also written P2BUN2208, P2B UN2 208, UNI II, UNI-II, Unisphere II.

How it locks to the shaft — and why that is the headline spec:
Unisphere II uses a Springlok concentric locking collar, not setscrews driven directly into the shaft. The collar clamps concentrically around the extended inner ring, so the grip is even all the way round and the shaft is not dimpled or scored. Three practical consequences. First, the shaft stays true, so the unit can be removed and re-fitted at the same position without chasing a raised burr. Second, concentric clamping holds far better than setscrews under reversing and shock loads, where setscrews walk loose over time. Third, because the grip is symmetrical there is no eccentric pull to induce runout at speed. If your original was a setscrew unit that kept creeping on the shaft, this locking style is the fix, not just a substitute. Note that some distributor data sheets for this part list “set screw” — that refers to the screws inside the locking collar, not screws bearing on the shaft.

Non-expansion — check this before you order two:
This is a fixed (non-expansion) unit: the insert is axially located in the housing, so it carries thrust and sets the shaft’s axial position. A shaft on two bearings needs exactly one located bearing and one free to float. Fit two non-expansion units on a long or hot shaft and thermal growth will load them axially against each other, which is one of the most common causes of premature mounted-bearing failure. Dodge indicates expansion variants with an E after the seal code.

Why spherical roller, not tapered or ball:
The double row of spherical rollers runs on a curved outer raceway, so the insert genuinely self-aligns — it accommodates mounting error, shaft deflection and thermal bowing while still carrying 39,000 lbf (173.5 kN) dynamic and 47,500 lbf (211.3 kN) static on a 2-1/2 in shaft. A tapered roller unit of this size would take more thrust but tolerates almost no misalignment; a ball unit self-aligns but carries a fraction of the load. Spherical roller is the middle answer, and it is why these units dominate screw conveyors, drag conveyors, bucket elevators and large fans. The trade is speed: 1,900 rpm maximum. Above that, use a ball unit.

Published ratings and mounting data:
Base to shaft centreline 2-3/4 in (69.85 mm). Bolt slots accept 5/8 in bolts and span 6.81 to 7.44 in (173.05 to 188.93 mm) centre to centre, nominally 7.1 in — that slot range is what lets the unit drop onto an existing base with slightly different hole spacing. Length through bore 2.203 in (55.96 mm), overall about 9-1/4 in long x 2.2 in wide x 5.69 in high on a 2.56 in wide base, two mounting holes, weight 13.4 lb (6.08 kg). Housing is a one-piece solid casting with a black oxide finish; sources differ on grade, listing it as either ductile iron or cast iron, so it is recorded here as iron rather than asserting one.

Lubrication and sealing:
Relubricatable through a grease fitting, factory charged with Mobilgrease XHP222. Single-lip contact seals. In dusty or wet service grease frequently and in small amounts to keep a slight purge at the seals; a big shot at long intervals will overheat the insert and still leave the seal dry between services.

Interchange guidance:
Dodge mounted bearings went Dodge → Rockwell/Reliance → Baldor Electric → ABB → Dodge Industrial (RBC Bearings, 2021). The catalogue numbers never changed, so P2B-UN2-208 and item 048008 remain the correct search terms whichever brand name is on the paperwork you inherited.