BK Series Drawn Cup Needle Roller Bearings

The same drawn cup with one end closed: the stamped cup is formed into a base, and that base — not a separate washer — is what the shaft end butts against, so the bearing also takes the axial location of whatever runs on it. It shares its boundary dimensions with the open-ended HK bearing of the same four digits, because ISO 3245 heads one table with both: a BK1210 is 12 mm across the needle complement, 16 mm outside and 10 mm wide, exactly like an HK1210, and the only difference in the part is which end is closed. Neither 12 nor 10 is a bore — Fw is the shaft diameter and C the width — and the outside diameter comes from the standard's table, not the designation.

One table, two ends. ISO 3245 heads a single boundary table with both forms of the drawn cup — "with open ends or one closed end" — so the BK and the HK of the same four digits are the same row of the same table: same Fw, same outside diameter, same cup width. What changes is the cup. In the BK one end is formed into a base, and the base is part of the cup rather than a washer pressed in afterwards, which is why the standard gives the closed form two extra figures for the bottom thickness and the open form none.

The closed end does two jobs. It retains the needle complement without a separate thrust washer, and it gives a shaft end a face to butt against, so a BK can take the axial location of the part running on it. That is also the limit of the claim: the base locates, it does not carry axial load the way a thrust bearing would, and the boundary dimension plan has nothing to say about how much axial load either form takes.

Reading the designation. BK1210 is BK, then 12, then 10 — Fw, the diameter the shaft has to be ground to, and C, the width of the cup. Neither is a bore code, neither is multiplied by five, and there is no dimension series in the designation at all. The outside diameter is not in it either: BK1210 is 16 mm across while BK1212 is 18 mm, and both come from the ISO 3245 table for the diameter series rather than from the number.

No chamfer column, and no clearance row. The chamfer minimum is in ISO 3245 but not in the catalogue tables consulted for this type, which print Fw, D and C only, so no second source exists for the cell and it is left out. The clearance row is missing for a reason of its own: ISO 5753-1 leaves drawn cup needle roller bearings out of its scope in as many words, so there is no table for this type in the standard this library takes its clearance figures from.

Where the BK list is thinner than the HK list. This library carries 38 BK sizes against 62 HK ones, and the gap is in the sources rather than in the standard: 37 sizes are confirmed in both forms, 25 in the open form only and 1 in the closed form only. A size is printed here only where two independent catalogues agree on Fw, D and C, so a form that one catalogue does not carry cannot be printed on the strength of that catalogue alone.

How far the series runs. BK0306 at the bottom and BK5020 at the top: an Fw of 3 to 50 mm, an outside diameter of 6.5 to 58 mm and a cup width of 6 to 38 mm. It stops short of the HK range at the top end, which is the sourcing rule again — the Fw values above 50 mm are confirmed in the open form only.

This series runs from a 3 mm to a 50 mm shaft. The sub-library as a whole reaches 300 mm of bore, and the widest single bearing in it is a 6360, 620 mm across, in the 6300 series. It shares its outside-diameter ladder with the complete bearings of the same dimension series.

Fw = needle complement diameter, D = outside diameter, C = width. All of them are ISO 3245 standard values and are the same for every manufacturer. C is the width of the cup. The outer ring of this type is a thin stamped shell rather than a machined ring, so there is one width to state and no inner ring to state one for: Fw is the diameter the shaft has to be ground to, D the outside diameter of that shell, and of the three only Fw and C appear in the designation. The last column is derived: radial section = (D − Fw) / 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. The 6 series whose type has no bore are not rows here: they are indexed by the shaft they run on, and their chart is above.