Fafnir9124KDDeep Groove Ball Bearing 120 x 180 x 28 mm, One Metal Shield, Conrad Non-Filling-Slot, Extra-Light Series

Product Description

What this part is

A Fafnir (now Timken) 9124KD single-row deep groove ball bearing, 120 mm bore × 180 mm outside diameter × 28 mm wide, with one pressed steel grease shield and the opposite face open. It is from the 9100 extra-light series, so it takes a large shaft in an unusually shallow cross-section. Made in USA. Despite sharing a supplier with Fafnir’s angular contact range, this is not an angular contact bearing — it carries radial load with only modest thrust in either direction.

Decoding the designation

9100 — Timken’s extra-light series. Bore code 24 = 120 mm (24 × 5).
K — Conrad (non-filling-slot) construction, with a high shoulder on both the inner and outer rings. This is what makes it a deep groove bearing rather than an angular contact one, and it is why the bearing takes thrust in both directions.
D — one steel-plate grease shield. Timken’s own Fafnir lettering system is explicit: “D — Steel Plate grease shield on one side of bearing”, and “DD — Shields on both sides of bearing.”

The suffix trap worth knowing about

Fafnir closure suffixes do not follow the industry convention, and reading them by habit will get you the wrong part. In Fafnir’s scheme D is one shield and DD is two; P is one seal and PP is two; L and LL are one and two Mechani-Seals; R and RR are land-riding rubber seals; T and TT are felt seals. The one that catches people is G: in Fafnir numbering G is the Wireloc snap ring — not a shield and not a seal at all. So 9124KG is a snap-ring bearing, 9124KD is this one-shield bearing, and they are different parts. Timken’s catalogue table for this size lists 9124KD, 9124P, 9124PP and 9124KG as available and shows no 9124KDD — a two-shield version of this bearing was never offered.

Confirming the source data

The source listing described this as a single metal shield, and that is correct on both counts — confirmed against Timken’s published suffix legend and against the bearing itself. The photographs show one face fully open, with the balls and the riveted two-piece pressed steel ribbon cage visible, and the opposite face closed by a plain pressed steel shield. The ring is etched FAFNIR 9124KD and MADE IN USA, and the carton label reads FAFNIR 9124KD USA. One correction of emphasis rather than of fact: the ISO analogue is 6024Z (one shield) and specifically not 6024ZZ or 6024-2Z, which are two-shield bearings.

What these specs mean in practice

The extra-light series is the whole point of this bearing. At 120 mm bore, a standard 6200-series equivalent would be considerably fatter and heavier; the 9100 series keeps the outside diameter to 180 mm and the width to 28 mm, which is what lets a large-diameter shaft run in a compact housing. You pay for that in load capacity — a thin section cannot carry what a medium series carries — so this is a bearing chosen for geometry first and load second. The single shield is a deliberate half-measure: it keeps coarse debris out of the ball track and holds the grease in on the side facing the dirty end of the machine, while the open face lets the bearing be relubricated in place and lets oil circulate through it from a shared sump. If you need contamination protection from both directions, one shield will not give it to you, and a two-shield version of this part does not exist — you would be looking at 9124P or 9124PP for seals instead.

Published ratings and mounting data

From Timken (cad.timken.com, 9124KD record, and Ball Bearing Catalog 10734, 9124K row):

Basic dynamic radial load rating C — 86,300 N (19,400 lbf)
Basic static radial load rating C0 — 73,100 N (16,400 lbf)
Limiting speed — 2,000 rpm grease, 2,331 rpm oil
Bearing weight — 2.2 kg (4.9 lb)
Bore tolerance — 120 mm, +0.000 / −0.020 mm
Outside diameter tolerance — 180 mm, +0.000 / −0.025 mm
Shaft backing shoulder diameter — 130 mm (5.1181 in)
Housing backing shoulder diameter — 169.90 mm (6.6890 in)
Maximum shaft fillet radius — 2.0 mm (0.079 in)
Shield thickness — 3.05 mm (0.120 in)
Rolling elements — steel balls; ball count and diameter are not published by Timken

A note on the numbers, because the two Timken sources do not agree. The printed catalogue gives the 9124K a static rating of 71,100 N (16,000 lbf) and an extended dynamic rating CE of 88,900 N (20,000 lbf). The CAD portal gives C0 = 73,100 N and C1 = 86,300 N. CE and C are different quantities — CE is an extended-life rating, not the conventional ISO 281 basic dynamic rating — so the CAD figures are the ones published above, and the catalogue’s 88,900 N is deliberately not presented as C. Precision class is left blank: Timken publishes no class for the unprefixed 9124K. The optional M and V prefixes buy ABEC 3 and ABEC 5 respectively, which implies the plain part is ABEC 1 / ISO P0, but Timken does not state it and we are not going to state it for them.

Condition

New old stock. The bearing has never been installed and spins freely, but it has been in storage: there are grease stains and light handling marks on the rings, visible in the photographs. It comes with its original plain brown carton, marked 1 EA, 321-001-0020 and 1D-39-F2 with a small FAFNIR 9124KD USA label — those first two are a distributor or end-user stock number, not Timken part numbers.

Fitting notes

Orient the shielded face toward the contamination source and the open face toward whatever will relubricate the bearing. Respect the backing shoulder diameters and the 2 mm maximum fillet radius above; on a thin-section bearing like this an oversized fillet or an undersized shoulder does real damage, because there is very little ring material to absorb a misaligned seat. Press only on the ring being fitted — never drive load through the balls — and never press against the shield, which is a light pressed-steel part that will deform and then rub. Given the age of the grease, check that the lubricant is still serviceable before putting it into a critical position, and consider a fresh charge through the open face.

Interchange guidance

The 120 × 180 × 28 mm envelope is the ISO 6024 boundary set, so 6024-series deep groove bearings from any maker will fit the same shaft and housing, and 6024Z (one shield) is the correct closure analogue — for example SKF 6024-Z, FAG 6024.Z, NSK 6024Z or NTN 6024Z. Be careful to specify a single shield: 6024ZZ, 6024-2Z and 6024-2RS are two-closure bearings and are not equivalent to a 9124KD. Note also that Timken itself does not publish “6024” as an equivalent designation for the 9124K — the 9100K series is its own line and the equivalence here is a dimensional and closure match rather than a manufacturer-published interchange. Related Fafnir variants at this size: 9124K open, 9124KG with a Wireloc snap ring, 9124P one seal, 9124PP two seals. Fafnir is a retired brand absorbed into Timken.