NU 23 Series Cylindrical Roller Bearings

The wide version of the NU 3, and the widest envelope in the cylindrical family here: same outside diameter as the NU 3 at every bore, in a wider ring — a NU2304 is 20 × 52 × 21 mm against 20 × 52 × 15 for the NU304, and a NU2315 is 75 × 160 × 55 against 75 × 160 × 37. Within the family that is where the load capacity is, and because the outside diameter stays on the NU 3 ladder it costs axial room rather than a bigger housing.

The widest of the four, on the medium ladder. The middle field of NU2304 is the dimension series 23: 2 for the width series, 3 for the diameter series. The diameter series is what sets the outside diameter, so the NU 23 stands on the NU 3's ladder and pays for its extra capacity in width alone. Put the family in order at a 20 mm bore and the four steps are plain: NU204 is 20 × 47 × 14 mm, NU2204 is 20 × 47 × 18 mm, NU304 is 20 × 52 × 15 mm and NU2304 is 20 × 52 × 21 mm — two outside diameters and two widths, and this series is the largest of each.

Why the NU 23 and the 2300 have the same numbers. The 2300 self-aligning family is the wide version of the medium series on the same two digits, so the two line up row for row: NU2304 is 20 × 52 × 21 mm and 2304 is 20 × 52 × 21 mm. At the top of the series NU2315 is 75 × 160 × 55 mm against 2315's identical figures, and against the NU315's 75 × 160 × 37 mm — the same shaft and the same housing bore for 18 mm more ring.

What the width buys. Radial capacity, and it is the cheapest way to get it. A wider ring gives a wider raceway and a longer roller path, so the bearing carries more radial load without any increase in outside diameter — the housing does not change at all. The price is axial room on the shaft, and in a cylindrical roller bearing that room has to be there anyway: a NU locates nothing along the shaft, so a shaft on NU bearings is free to float and the width is usually easier to find than a larger housing.

Reading the designation. NU2304 is the type code N, the structure letter U, the dimension series 23 and the bore code 04. The width series is written here, unlike in the NU 2 and NU 3 series where it is 0 and left out. The bore code reads as it does throughout: 00, 01, 02 and 03 are 10, 12, 15 and 17 mm, and from 04 upwards the code multiplies by five. NU, NJ, NUP, N and NF share this table exactly as they share the other three.

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 75 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.