NU 3 Series Cylindrical Roller Bearings

The medium cylindrical roller series — diameter series 3, one step larger across and wider than the NU 2 at the same bore: a NU304 is 20 × 52 × 15 mm against 20 × 47 × 14 for the NU204, and a NU310 is 50 × 110 × 27 against 50 × 90 × 20 for the NU210. That extra envelope is what buys radial capacity, so this is the series a gearbox or a mill stand steps up to when the NU 2 is running out of rating. The same five structure letters — N, NU, NJ, NUP, NF — share this table, exactly as they do in the light series.

Reading the designation. NU304 is the type code N, the structure letter U, the diameter series 3 and the bore code 04 — four fields, with the width series 0 left unwritten. The 3 is the same diameter series a 6304's middle digit names, and that is the whole reason the two families share their outside diameters. The bore code is the familiar one: 00, 01, 02 and 03 are 10, 12, 15 and 17 mm, and from 04 upwards the code multiplies by five.

Why the NU 3 and the 6300 have the same numbers. Diameter series 3 on both sides, so the tables run in parallel the whole way: NU304 is 20 × 52 × 15 mm and 6304 is 20 × 52 × 15 mm, and at the top of the series NU315 is 75 × 160 × 37 mm against 6315's identical figures. The 1300 self-aligning series is on that same rung as well — a 1304 is 20 × 52 × 15 mm — so three different bearings, a ball bearing and two kinds of roller bearing, fit the same seat.

The step up from the NU 2. Medium against light is the ordinary step from one diameter series to the next: at a 20 mm bore, 52 mm across against 47, and 15 mm wide against 14. At a 50 mm bore the gap is much wider — a NU310 is 50 × 110 × 27 mm where a NU210 is 50 × 90 × 20 mm — and that extra envelope is what buys radial capacity. This is the series a gearbox or a mill stand steps up to when the NU 2 has run out of rating and the housing can be enlarged.

What the type buys, and what it costs. Line contact instead of point contact, so several times the radial load of a deep groove ball bearing in the same envelope, and at this diameter series a good deal more than the NU 2 as well. The cost is the same as in the light series: a NU locates nothing along the shaft, so it needs a companion bearing to hold the shaft in position. NU, NJ, NUP, N and NF share this d / D / B table exactly as they share the light one.

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.