Koyo6310 C2 FY P5Precision Deep Groove Ball Bearing, Open, Machined Brass Cage, ABEC 5, C2 Tight Internal Clearance, 50 x 110 x 27 mm

Product Description

What this part is

A precision single-row deep groove ball bearing in the metric 6300 medium series, 50 mm bore × 110 mm outside diameter × 27 mm width. Open on both sides, fitted with a machined brass cage, held to ABEC 5 running accuracy, and supplied with C2 radial internal clearance, which is tighter than standard. The combination suits a spindle, a grinding head, or a high-speed shaft carrying a precision tool or rotor.

Designation breakdown

Koyo publishes its own nomenclature guide, which decodes this part number. The suffix order in Koyo’s worked example is series, bore, closure, clearance, retainer, tolerance, grease, which is the order 6310 C2 FY P5 follows. 6300 series: metric, single row, medium series, the heavier of the common cross-sections, which is why a 50 mm bore carries a 110 mm outside diameter here rather than the 90 mm of a 6210. 10: bore code; for codes 04 and above, bore = code × 5, so 10 × 5 = 50 mm. No closure code: open, Koyo printing Z or ZZ for shields, RS or 2RS for contact seals and RU or 2RU for non-contact seals. C2: radial internal clearance smaller than standard, with C1 smaller still, no code standard, and C3 and C4 progressively larger. FY: machined brass retainer, confirmed physically by the yellow-gold machined cage with visible rivets in the photographs. P5: ABEC 5 precision, Koyo’s scale running no code = ABEC 1, P6 = ABEC 3, P5 = ABEC 5, P4 = ABEC 7. No grease code: consistent with an open bearing shipped dry apart from its preservative, Koyo printing XM, SR, A2 or P2 when a grease is charged.

C2 internal clearance

C2 is tighter than the standard CN class. Tighter mounted clearance seats the balls more firmly against both raceways, so more balls share the load at any instant and the bearing is stiffer both radially and axially, with less runout and less noise. That pairing is why C2 and P5 are specified together here.

Clearance is consumed rather than fixed. An interference fit on the shaft expands the inner ring, a tight housing fit compresses the outer ring, and in service the inner ring usually runs hotter than the outer and grows more. A C2 bearing starts with less clearance to give away. At zero residual clearance the bearing runs preloaded, friction rises, the bearing heats, the inner ring grows further and friction rises again, so C2 belongs in an application with a modest ring-to-ring temperature difference and specified fits rather than a hot pump end or a motor with heavy interference and a large thermal gradient. At excessive clearance the load is carried by too few balls, contact stress climbs and the balls skid rather than roll, which scuffs the raceways and shows as noise and vibration.

Machined brass cage

A machined brass cage is the traditional heavy-duty, high-speed precision choice. It is dimensionally stable, tolerant of temperatures that soften a polymer cage, resistant to most lubricants including aggressive synthetics, and stiff enough to resist the centrifugal ballooning that limits pressed steel cages at speed. It runs quietly and survives handling. Brass is heavier than steel or polymer, so it contributes more to imbalance and to cage-pocket friction at very high speed, and it costs more than the pressed steel in a commodity 6310.

ABEC 5 precision class

ABEC 5 (P5) tightens the tolerances on bore, outside diameter and width, and above all on the radial and axial runout of the assembled bearing, against the ABEC 1 / Normal class. It does not raise load capacity. What it provides is positional accuracy and quiet, repeatable running: a surface finish held on a machine tool, less chatter in a grinding head, less bearing-induced imbalance in a high-speed rotor. The result tracks the accuracy of the shaft and housing seats.

Published dimensions and ratings

Bore d: 50 mm. Outside diameter D: 110 mm. Width B: 27 mm. Bearing type: single row deep groove ball bearing, open, 6300 medium series. Internal clearance: C2, smaller than standard. Precision class: ABEC 5 / P5. Cage: machined brass, riveted. Basic dynamic load rating C: 77.5 kN, distributor-published. Basic static load rating C0: 38.3 kN, distributor-published.

Quantity and configuration

One bearing, in its original Koyo carton. This is a single bearing rather than a matched or preloaded pair: the designation carries no pairing or preload code, and deep groove ball bearings are not universally ground for pairing the way angular contact bearings are.

Mounting data

Bore 50 mm, outside diameter 110 mm, width 27 mm, straight bore. Mounting force passes through the ring being fitted, the inner ring onto the shaft and the outer ring into the housing, and not through the balls. Shaft and housing seats follow the fits given on the spindle drawing; with C2 clearance an interference fit 20 microns tighter than specified takes the mounted clearance to zero on its own. A brass cage is the most tolerant of the common cage materials to heat mounting. The bearing ships dry apart from its preservative and is lubricated with the oil, oil-mist or grease specified for the spindle.

Interchange guidance

Dimensionally, 50 × 110 × 27 mm is the ISO 15 standard 6310 envelope, so any 6310 from any manufacturer fits the same seats, including SKF, FAG, NSK, NTN, NACHI, Timken and Fafnir. A specification match takes all three of a P5 / ABEC 5 tolerance class, C2 internal clearance and a machined brass cage. In SKF and FAG notation that combination reads roughly 6310 M/C2 P5, where M denotes the machined brass cage; NSK and NTN express it as 6310 M C2 P5. SKF’s related codes distinguish MA (outer-ring guided) from MB (inner-ring guided), whereas Koyo’s FY specifies the brass machined retainer without stating which land guides it, so a Koyo FY and an SKF MB are close cousins rather than identical parts, and the 6310 C2 MB P5 designation is carried here as a searchable equivalent.

Koyo bearing production now sits under JTEKT, so current-production equivalents appear under the JTEKT Koyo brand. A related precision-spindle alternate is the SKF 6214 TC/C78, an open ABEC 5 precision deep groove ball bearing, 70 × 125 × 24 mm, with a machined phenolic cage, under SKU B-AH6B2#OXHSM7.