688 Bearing Dimensions: 8x16x4mm Open, 5mm Sealed

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Reviewed by MLC Editorial Team | 16 August 2026

Verified by Rachel Mayfield, Supply Chain Analyst - August 2026

The 688 is a single-row deep groove ball bearing measuring 8x16x4 mm open (5 mm sealed) (bore x outside diameter x width). Those boundary dimensions come from ISO 15, so a 688 from SKF, NSK, NTN, EZO, NMB or any budget brand is dimensionally interchangeable - the differences are in materials, precision grade, internal clearance and seal design, not size.

688 bearing dimensions

Property	Value	Standard
Bore diameter (d)	8 mm	ISO 15
Outside diameter (D)	16 mm	ISO 15
Width (B), open	4 mm	ISO 15
Width (B), ZZ / 2RS	5 mm	manufacturer standard
Bearing type	Single-row deep groove ball bearing	ISO 15
Dimension series	680 miniature thin section	ISO 15

Always measure a worn bearing before ordering if the number is unreadable: bore with calipers on the inner ring, outside diameter across the outer ring, and width across either ring face. 8x16x4 mm open (5 mm sealed) identifies the 688 uniquely among common metric sizes.

Open and sealed 688 bearings have different widths

This is the detail that catches people out, and plenty of listings get it wrong. The open 688 is 4 mm wide per ISO 15. The shielded (688ZZ) and sealed (688-2RS) versions use an extended inner ring to carry the shield or seal, taking the width to 5 mm. Some sellers list the sealed width as if it were the only one. If your assembly was designed around one width, fitting the other changes the stack-up - measure the old bearing's width before ordering, not just bore and outside diameter.

What the suffixes mean (688ZZ, 688-2RS, 688-C3)

Suffix	Meaning	When to choose it
ZZ / 2Z	Metal shield both sides	Non-contact, low friction, keeps debris out. Not washdown-proof.
2RS / 2RS1 / DDU / LLU	Rubber seal both sides	Contact seals, best dirt and moisture exclusion, slightly more friction.
Z / RS	Shield or seal one side only	Open on the other side - used where relubrication is needed.
Open (no suffix)	No seals or shields	For housings with their own sealing and external lubrication.
C3	Extra internal clearance	For motors and anywhere the inner ring runs hotter than the outer.
2RS-C3	Sealed + C3 clearance	The standard electric-motor spec.

Brand equivalents for the 688

Every major manufacturer makes the 688. The seal and shield codes differ by brand but the bearings interchange directly:

Brand	Shielded version	Sealed version
SKF	688-2Z	688-2RSH
FAG (Schaeffler)	688-2ZR	688-2RSR
NSK	688ZZ	688DDU
NTN	688ZZ	688LLU
Koyo (JTEKT)	688ZZ	688-2RS

Load ratings: check the maker's catalogue

Dynamic (C) and static (C0) load ratings for the 688 differ between manufacturers and between standard and premium ranges, so MLC does not publish a single figure. Look the value up in the manufacturer's own catalogue for the exact variant you are buying - SKF, Schaeffler medias, NSK and NTN all publish free online catalogues with per-variant ratings, limiting speeds and grease specifications.

Where the 688 is used

The 680 miniature thin section family is the smallest thin-section family - open and sealed versions have DIFFERENT widths, which catches a lot of buyers out. Typical 688 applications include RC cars, e-scooters, fishing reels and micro machinery - the most produced 68x size.

Fitting basics

For a rotating shaft (the normal case), fit the inner ring with a light interference fit and the outer ring with a close clearance fit (H7 housing for most machinery). Press only on the ring you are fitting - pressing the outer ring through the balls to seat the inner ring is the fastest way to brinell a new bearing. For sealed 2RS variants, no relubrication is needed or possible; the factory grease fill is for life.

References

Need this bearing? Send the designation and quantity and Acumen Seals & Pumps will price it, including sealed, shielded and equivalent options.

Get a quote for 688 Bearing Dimensions: 8x16x4mm Open, 5mm Sealed

Acumen Seals & Pumps - UK specialist in mechanical seals, FFKM O-rings, Kalrez compounds, and elastomer parts. 36 years of inventory, UK stock with 24-48 hour despatch, and a price back within 4 working hours.

Send an enquiry via the MLC contact form

Frequently Asked Questions

What size is a 688 bearing?

A 688 bearing measures 8 mm bore x 16 mm outside diameter. The open version is 4 mm wide and the shielded or sealed version is 5 mm wide - the two widths differ on this size.

What does 688-2RS mean?

The 2RS suffix means the 688 has rubber contact seals on both sides. It keeps grease in and dirt and moisture out, and is the right choice for most machinery. ZZ means metal shields instead - lower friction but less sealing.

Are 688 bearings interchangeable between brands?

Yes. The 688's dimensions are standardised for every maker, so an SKF 688 swaps directly with NSK, NTN, Koyo or EZO. Match the suffix too: SKF 2RSH, NSK DDU and NTN LLU are all the sealed version.

What is the C3 suffix on a 688 bearing?

C3 means greater-than-normal internal clearance. Electric motors and hot-running applications use C3 because the inner ring expands more than the outer in service; standard clearance would leave the bearing too tight when warm.

Independent UK engineering trade publication. Company profiles cross-referenced with Companies House.

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Get a UK price for a 688 bearing

Andrew Sykes at Acumen Seals & Pumps — 36 years supplying UK industry. Send the designation and he will source it, including sealed, shielded and equivalent options.

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