Fafnir5305KDouble-Row Angular Contact Ball Bearing, Open, 25 x 62 x 25.4 mm, 20 Degree Contact Angle, Nylon Cage

Product Description

What this part is

The 5305K is a double-row angular contact ball bearing, 25 mm bore x 62 mm outside diameter x 25.400 mm (1 in exactly) wide — the 3305 envelope.

Two rows of balls run on a single one-piece inner ring and a single one-piece outer ring, which is functionally a back-to-back duplex pair built into one part. That gets you radial capacity, thrust capacity in BOTH directions and real moment stiffness inside one bearing width, and it removes the commonest assembly mistake on a duplex pair — fitting one of the two bearings the wrong way round.

Published ratings and mounting data

Rated 7,700 lbf dynamic and 4,750 lbf static, with a maximum speed of 6,900 rpm and a working range of -50 to 120° C.

Decoding the designation

The K suffix has a specific meaning in Fafnir’s lettering system: Conrad, non-filling-slot construction. A Conrad-type bearing is assembled by displacing the rings and dropping the ball complement in, so there is no loading slot notched into the ring shoulders. No slot means an uninterrupted raceway shoulder and no stress-raising step, which is why Conrad construction runs quieter and is preferred where the bearing sees reversing thrust. The trade-off against a filling-slot maximum-capacity type is a smaller ball complement and therefore less radial capacity for the same envelope.

What these specs mean in practice

Contact angle is 20°, and this is the number that decides whether a substitution is valid. Check it brand by brand: the Fafnir/Timken 5300 series runs 20°, whereas MRC’s 5300 series on the identical 25 x 62 x 25.4 mm envelope runs 30°. Both will drop into the same housing and onto the same shaft; they are not the same bearing in duty. A shallower 20° angle favours radial capacity and speed, a steeper 30° angle favours thrust capacity and axial stiffness. Match the angle to the load case, not the tape measure.

The cage is moulded nylon. On a bearing of this size and speed a polymer cage is lighter and quieter than a pressed steel one, and it tolerates marginal lubrication better than steel because it will not gall against the balls. It is the temperature limit that comes with it — which is what sets the 120° C ceiling — so this is not the part for a hot bearing position where a steel or bronze cage would be specified instead.

The bearing is OPEN: no seals, no shields, no snap ring. That means it relies on the housing for sealing and for its lubricant supply, so it belongs in an enclosed, oil-fed or grease-packed housing rather than an exposed position. If you need the bearing to carry and keep its own grease in a dirty environment, a sealed variant is the correct choice instead.

Quantity and configuration

Sold as one bearing.

Interchange guidance

The outer ring is marked FAFNIR, 5305K and USA. The ISO cross-reference for this envelope is 3305. Fafnir is now part of Timken, so current-catalogue equivalents carry Timken numbering. Also written 5305-K, 5305 K and FAF5305K.