51100 Series Thrust Ball Bearings

The light thrust series, and the one this name usually means: a 51104 is 20 mm bore, 35 mm outside diameter, 10 mm high. A thrust ball bearing is three separate parts — a shaft washer, a ball and cage set, and a housing washer — and it carries axial load in one direction only, with no radial capacity at all. The same bore as a 6204 therefore does not make it a substitute for one: the numbers describe a mounting envelope, not a function. H is the height of the assembled stack.

A thrust ball bearing is not a radial bearing that happens to be flat. It is three separate components — a shaft washer, a ball and cage set, and a housing washer — stacked along the axis, and it takes axial load in one direction only. There is no radial capacity in it whatsoever: if the shaft needs radial location as well, that has to come from another bearing somewhere in the assembly. The same bore as a 6204 therefore makes a 51104 a companion to it, never a substitute for it.

That is why ISO 104 specifies this type with H rather than a width. H is the height of the assembled stack — the axial space the three components occupy together — and it is the only one of the three dimensions where a thrust bearing differs in kind from the rest of this library. A 51104 is 20 × 35 × 10 mm; the 10 mm is not a ring width and not a raceway width, it is the envelope of a shaft washer, a ball set and a housing washer sitting on top of each other. The bore and the outside diameter still mean exactly what they mean everywhere else.

The series runs from 51100 (10 mm bore, 24 mm outside diameter, 9 mm high) to 51120 (100 mm bore, 135 mm outside diameter, 25 mm high), and it covers every bore code from 00 to 20 without a gap — the bore-code exceptions included, so the 51100 is a 10 mm bore and the 51101 a 12 mm one. The progression is worth looking at before designing with one: over that whole range the outside diameter grows by a factor of more than five while the height grows by under three, because the washers get bigger rather than the stack getting deeper.

Every designation in the table below links to its own page with the ISO 104 dimensions, the bore-code arithmetic, the same-bore comparison against every series of all three types — including the ball and tapered bearings that take the same shaft but do a different job — and a section explaining why a thrust ball bearing has no radial internal clearance to state.

This series runs from a 10 mm to a 100 mm bore. The sub-library as a whole reaches 200 mm, and the widest single bearing in it is a 6340, 420 mm across, in the 6300 series. This one stops short of it.

d = bore diameter, D = outside diameter, H = bearing height. All of them are ISO 104 standard values and are the same for every manufacturer. H is the height of the assembled stack, not the thickness of one washer: a thrust ball bearing is a shaft washer, a ball and cage set and a housing washer, and ISO 104 fixes only the envelope the three of them occupy together. 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.