Brand: NSK

NSK 51208 Thrust Ball Bearing

Name: NSK 51208 Thrust Ball Bearing – Catalog & Quote
Brand: NSK
SKU: 51208

Description

A single-direction thrust ball bearing for vertical shafts and axial loads

The NSK 51208 is a single-direction thrust ball bearing with a 40 mm bore, 68 mm outside diameter and 19 mm height. It consists of a shaft washer, a housing washer with a flat seat and a ball and cage assembly, and it carries axial load in one direction only. NSK states plainly that thrust ball bearings can sustain axial loads but no radial loads, so a radial bearing must locate the shaft. They are used on vertical pump shafts, turntables, crane hooks, jack screws and swivel units where the axial load is steady in one direction and speed is moderate, as the limiting speeds below show. The cage is pressed steel in this size.

Technical specifications

Parameter	Specification
Designation	51208: 5 = thrust ball bearing, 12 = diameter series 2 (512), 08 = 40 mm bore
Bore d / outside D / height T	40 mm / 68 mm / 19 mm
Chamfer r (min.)	1 mm
Basic dynamic axial load rating Ca	47,500 N
Basic static axial load rating C0a	98,500 N
Limiting speed, grease / oil	2,800 rpm / 4,300 rpm
Mass (approx.)	0.27 kg
Housing washer seat	Flat seat (51208); aligning seat 53208 (0.289 kg); aligning seat with seat washer 53208U (0.355 kg)
Cage	Pressed steel for 51200 to 51236X; machined brass for larger sizes
Load direction	Axial only, one direction; no radial load capacity

Size table for the NSK 512 series

Rows are the single-direction flat-seat bearings of diameter series 2 from the NSK thrust ball bearing table.

Designation	d mm	D mm	T mm	Ca N	C0a N	Grease rpm	Oil rpm	Mass kg
51204	20	40	14	22,500	37,500	4,300	6,300	0.077
51205	25	47	15	28,000	50,500	3,800	5,600	0.111
51206	30	52	16	29,500	58,000	3,400	5,300	0.137
51207	35	62	18	39,500	78,000	3,000	4,500	0.21
51208	40	68	19	47,500	98,500	2,800	4,300	0.27
51209	45	73	20	48,000	105,000	2,600	4,000	0.31
51210	50	78	22	49,000	111,000	2,400	3,600	0.378
51211	55	90	25	70,000	159,000	2,200	3,200	0.599
51212	60	95	26	71,500	169,000	2,000	3,000	0.673

Seat types and care in use

NSK divides single-direction thrust ball bearings into flat-seat types (51200 and the like), aligning-seat types (such as 53208) and aligning types with a seat washer (53208U), depending on the shape of the housing washer. Aligning seats absorb a small shaft misalignment, while the seat washer version allows alignment without machining a spherical housing. Double-direction bearings in the 52 series use the same cages as the single-direction bearings of equal diameter series. The cage is pressed steel up to 51236X and machined brass for larger sizes.

A thrust bearing needs a minimum axial load at all times, otherwise the balls slip against the raceways and the bearing wears. NSK refers readers to its technical section for the minimum axial load calculation, and limiting speeds are low because of centrifugal ball forces. The radial bearing that locates the shaft is often a deep groove type such as the SKF 6206-2RS1; browse Electric Motors, Pumps and Turbines.

Check the mounting orientation before fitting. The washer with the smaller bore is the shaft washer and the washer with the larger bore is the housing washer, which must sit with radial clearance in its seat so the load stays purely axial. Fitting the pair the wrong way round is a common cause of early wear.

Documents and ordering

Confirm the load direction, whether a flat seat, aligning seat or seat washer version is needed, the shaft and housing fits and the axial load level. The attached PDF is a page extract from NSK catalogue Rolling Bearings for Industrial Machinery (Cat. No. E1103b) with the thrust ball design notes and bearing tables. Seven Star LLC is an independent supplier in Muscat; availability is confirmed per enquiry.

Datasheets & Documents

Catalog NSK Rolling Bearings for Industrial Machinery E1103b - extract: single-direction thrust ball bearings, 512 series Download

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About brand

NSK Ltd. was founded in 1916 and is headquartered in Tokyo, Japan. The company, originally Nippon Seiko, makes bearings, automotive components and precision machinery, and its bearing range runs from miniature ball bearings to large industrial roller bearings, plus super precision bearings for machine tool spindles and ball screw supports. Seven Star LLC is an independent supplier in Oman and lists NSK catalogue models for maintenance teams, workshops and machine builders.

NSK bearing types

NSK publishes deep groove, angular contact, four-point contact, cylindrical roller, tapered roller and thrust ball bearings, bearing units and super precision series in its catalogues. Each product page here quotes dimensions, load ratings and limiting speeds as printed in the relevant NSK catalogue and links an extract of the catalogue pages.

Ordering NSK bearings: what we need

Give the complete designation marked on the bearing, including prefix and suffix letters such as seal, cage, clearance and precision codes. If the marking is worn, measure bore, outside diameter and width and tell us the machine and shaft position, the operating speed and the lubrication. State the quantity and any precision class or special clearance required.

Browse NSK products by category: Electromotors.