Omron E69-C68B Shaft Coupling for Rotary Encoders — 6 mm to 8 mm Different-End-Diameter Design

Part Number: E69-C68B 

Manufacturer: Omron 

Series: E69 

Type: Shaft Coupling — Different End Diameter 

Bores: 6 mm × 8 mm 

Material: Glass-reinforced PBT + Brass Bushings 

Compliance: RoHS

Getting a rotary encoder mounted cleanly onto a machine shaft sounds simple — until the shaft diameter doesn't match. The Omron E69-C68B is the coupling that solves exactly that problem: a purpose-designed shaft coupling accessory from Omron's E69 series that bridges a 6 mm encoder shaft to an 8 mm machine shaft, letting engineers connect their E6-series rotary encoders to a wider range of equipment without resorting to custom adapters or improvised solutions.

Small part. Significant function.

What This Coupling Does

Every rotary encoder needs a mechanical connection between its own shaft and the rotating component it's measuring. On paper, that's just a coupling. In practice, it's the component that determines whether your position feedback stays clean and accurate over thousands of operating hours — or introduces vibration, radial runout, and premature encoder bearing wear.

The E69-C68B is a different-end-diameter coupling, meaning one bore accepts the 6 mm encoder shaft while the opposite end accommodates an 8 mm drive shaft. This asymmetric design is specifically engineered for situations where the encoder and the shaft it needs to couple with are different diameters — a common real-world scenario in retrofit installations, system upgrades, or multi-source machine designs.

Technical Specifications

Compatible Omron Encoder Models

The E69-C68B is validated for use with the following Omron rotary encoder series:

• E6B2-C — 40 mm diameter incremental encoder
• E6C2-C — 50 mm diameter incremental encoder
• E6C3-C — 50 mm diameter incremental encoder
• E6D-C — incremental encoder series
• E6CP-A — absolute encoder (cam positioner type)
• E6C3-A — absolute encoder series

If your application uses any of these models with a machine shaft running at 8 mm diameter, the E69-C68B is the correct Omron accessory for the connection.

Design Choices Worth Understanding

Glass-reinforced PBT resin body. Some engineers instinctively reach for metal couplings, but for rotary encoder applications the lightweight resin construction is deliberate. A lower-mass coupling means lower moment of inertia, which reduces the rotational load placed on the encoder's internal bearings. Less bearing load translates directly to longer encoder service life — particularly relevant on axes that reverse direction frequently or accelerate sharply.

Brass bushings at both bores. The set screw points bear against brass inserts rather than directly on the plastic body. This concentrates clamping force effectively, prevents deformation of the bore over time, and maintains grip on both shafts without developing play as the coupling ages.

Four M4 hexagonal set screws. Two per bore side. The hex-key fastening provides controlled, even clamping pressure around each shaft. Unlike friction-only couplings, the set screws positively retain the coupling against axial pull-out, which matters in applications where vibration or shaft runout could otherwise work a press-fit loose over time.

Where This Coupling Gets Used

The E69-C68B shows up wherever Omron E6-series encoders need to connect to equipment with 8 mm shafts:

Conveyor and material handling lines — connecting E6B2-C or E6C2-C encoders to conveyor roller shafts for speed and position tracking

Packaging machinery — feeding axis position feedback where the machine shaft is 8 mm and the encoder is 6 mm

Motor test benches — mounting encoders onto motor output shafts for speed verification

Cam positioner systems — coupling E6CP-A absolute encoders to process machinery for rotary cam position monitoring

Retrofit and upgrade projects — replacing worn or damaged couplings on existing encoder installations without changing the encoder or the machine shaft

Sourcing Note

The E69-C68B is a standard catalog item in Omron's encoder accessory range. For installations requiring a different shaft size pairing — such as 6 mm encoder to 10 mm machine shaft — the E69-C610B covers that combination. The full E69 coupling family addresses multiple encoder-to-shaft diameter combinations within the same E69 series design standard.

FAQ

Q1: Is the E69-C68B a rotary encoder, or an encoder accessory?

It is a shaft coupling accessory — not an encoder itself. The E69-C68B is designed to mechanically connect an Omron rotary encoder (6 mm shaft) to a machine shaft (8 mm) so that the encoder can measure the rotation of the connected equipment. It belongs to Omron's E69 accessory series.

Q2: Which side of the coupling connects to the encoder and which to the machine shaft?

The 6 mm bore connects to the encoder shaft, and the 8 mm bore connects to the machine or drive shaft. Both ends are secured using M4 hexagonal set screws — two per bore side — which are tightened with a hex key after alignment.

Q3: Why is the coupling body made of resin rather than metal?

The glass-reinforced PBT resin construction keeps the coupling lightweight, which minimizes moment of inertia and reduces the mechanical load on the encoder's internal bearings. This extends encoder service life. The brass bushings in each bore provide the clamping durability where it's actually needed, without adding unnecessary mass to the rotating assembly.

Q4: Can the E69-C68B be used with Omron encoders other than those listed?

Omron's compatibility table specifically validates the E69-C68B for the E6B2-C, E6C2-C, E6C3-C, E6D-C, E6CP-A, and E6C3-A encoder models. Using it with encoders outside this list is not recommended unless the shaft diameter, flange geometry, and mounting arrangement have been independently confirmed to be compatible.

Q5: What is the difference between the E69-C68B and the E69-C610B?

Both are different-end-diameter couplings in the E69 series. The E69-C68B bridges a 6 mm encoder shaft to an 8 mm machine shaft. The E69-C610B bridges a 6 mm encoder shaft to a 10 mm machine shaft. Select the model that matches the actual diameter of your machine-side shaft.