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.