NTN HMK1720 C Nadelhülsen (17x24x20)

As a needle roller bearing, this bearing carries high radial loads in a very compact section. This NTN bearing measures 17x24x20 mm and weighs 0.028 kg; the specification table carries the supplementary technical details. Where every tenth of a millimetre counts radially — on gear shafts, rocker arms and pump rotors — that is the reason for this design.

The drawn cup needle roller bearing consists of a thin-walled, drawn steel cup with a needle set guided inside it. Because the cup does not form a solid ring but is produced by forming and pressed into the housing bore, this design achieves the smallest radial section height of all needle bearing arrangements: the space a bearing position otherwise takes up radially shrinks to little more than the needle diameter.

The decisive mounting condition follows from this at the same time. The cup is so thin that it takes on the form of its surroundings — after pressing in, the housing bore determines the raceway geometry and must therefore be closely toleranced, accurate in form and sufficiently load-bearing; a bore that is too wide, out of round or too soft enters directly into the running behaviour of the needle set.

Without an inner ring of its own, the needle set runs directly on the shaft, whose surface is thereby the raceway and has to be treated like a bearing component in hardness, surface finish and tolerance; where that cannot be realised, a separate inner ring is used. The design takes no axial force, so axial location has to be solved separately, and because of the long contact line of the needles the bearing position tolerates only slight misalignment between shaft and bore.

This version is supplied without a sealing element: lubricant supply, initial filling and protection against contamination are handled by the construction it is mounted into.