NU 2 Series Cylindrical Roller Bearings

The light cylindrical roller series: NU204 is 20 mm bore, 47 mm outside diameter, 14 mm wide, and the series runs to NU219 at 95 × 170 × 32. The 2 is the diameter series, and the letter before it is not decoration — N, NU, NJ, NUP and NF are five different flange arrangements that share this same d/D/B table. A NU204, a NJ204 and a NUP204 fit the same shaft and the same housing; they differ only in which direction they can locate the shaft. What the type buys over a ball bearing is line contact instead of point contact, which is why a cylindrical roller of this size carries several times the radial load of a 6204.

Reading the designation. A NU204 is four fields, not three: N is the type code for a single-row cylindrical roller bearing, U is the structure letter, 2 is the diameter series and 04 is the bore code. The width series is 0 and is never written, so the digit between the letter and the bore code is a diameter series on its own — the same rung a 6204's middle digit names. The bore code reads exactly as it does everywhere else: 00, 01, 02 and 03 are 10, 12, 15 and 17 mm, and from 04 upwards the code multiplies by five, which is why 04 gives 20 mm.

Why the NU 2 and the 6200 have the same numbers. The 2 is the diameter series, so the two families sit on the same rung of the same outside-diameter ladder and one table is a row-for-row copy of the other: NU204 is 20 × 47 × 14 mm and 6204 is 20 × 47 × 14 mm, all the way down to NU219 at 95 × 170 × 32 mm against 6219's identical three figures. That cuts both ways in practice — a housing bored for a 6204 will take a NU204, and a NU204 ordered as a replacement arrives at the same size and a different bearing.

What the U is doing there. NU is not the only cylindrical roller bearing. NJ, NUP, N and NF are the same bearing with the ribs moved: NU carries two ribs on the outer ring and none on the inner, NJ adds a single rib to the inner ring, and NUP adds a loose collar on top of that so the shaft can be located in both directions. All five share the same d / D / B table — a maker's catalogue prints them on one row — which is why one dimension table here covers all five even though every designation in it is NU. The letter is a statement about the ribs, not about the size.

What the type buys, and what it costs. Line contact instead of point contact: a roller meets its raceway along a line where a ball meets it at a point, and that is why a cylindrical roller bearing of this size carries several times the radial load of a 6204 in the same envelope. The cost is that a NU locates nothing along the shaft — the rollers are free to slide axially — so it needs a second bearing to hold the shaft in position, and it is the wrong choice where the bearing itself has to take axial load.

Every designation in the table below links to its own page with the ISO 15 dimensions, the bore-code arithmetic, the radial internal clearance ranges ISO 5753-1 gives for this type, and the same-bore comparison against every other series and type.

This series runs from a 20 mm to a 95 mm bore. The sub-library as a whole reaches 300 mm, and the widest single bearing in it is a 6360, 620 mm across, in the 6300 series. This one stops short of it.

d = bore diameter, D = outside diameter, B = width. All of them are ISO 15 standard values and are the same for every manufacturer. B is the width of a single ring, because the two rings are flush: this type states the same three dimensions a deep groove ball bearing does, with a different bearing inside the same envelope. No chamfer column appears because ISO 15 gives this type a separate chamfer minimum for each ring, and only one of the sources checked here prints both — which is not enough for this library to publish. The last column is derived: radial section = (D − d) / 2, the wall thickness you are working with when you size the housing. No load rating and no limiting speed appears here — see the bearings index for why.

Outside diameter × overall size in millimetres, for the 5 smallest bores in this database. The full charts, one per type, are on the bearings index. Reading a row is what a machine designer does when the shaft is already fixed: the bore does not change, the housing bore does. Across the type boundary the last number changes meaning — it is a width above and a height below — so compare within a type, then decide whether the job wants a ball bearing, a tapered roller or a thrust bearing at all.