$183.82 ea
Quantity Price (USD)
1 $183.82 ea
10 $110.29 ea
25 $91.91 ea
50 $82.72 ea
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Built to Order Lead Time: 0-2 Days
Ruland BCK21-10-6-A, 5/8" x 3/8" Bellows Coupling, Aluminum, Clamp Style With Keyway, 1.313" OD, 1.688" Length


Ruland BCK21-10-6-A is a bellows coupling with 5/8" x 3/8" bores, 1.313" OD, 1.688" length, and 3/16" x 3/32" keyways. It is zero-backlash and has a balanced design for reduced vibration at high speeds. BCK21-10-6-A is comprised of two anodized aluminum hubs and a stainless steel bellows. The bellows are able to flex while remaining rigid under torsional loads allowing for all types of misalignment to be accommodated. This bellows coupling is lightweight and has low inertia making it suitable for applications with speeds up to 10,000 RPM. Hardware is metric and tests beyond DIN 912 12.9 standards for maximum torque capabilities. Ruland manufactures BCK21-10-6-A to be torsionally rigid and an excellent fit for precise positioning stepper servo applications as well as encoders. It is machined from solid bar stock that is sourced exclusively from North American mills and RoHS2 and REACH compliant. BCK21-10-6-A is carefully manufactured in our Marlborough, MA factory under strict controls using proprietary processes.



Large Bore B1

0.625 in

Small Bore B2

0.375 in

Keyway K

3/16 in

Keyway K2

3/32 in

B1 Shaft Penetration

0.804 in

B2 Shaft Penetration

0.804 in

Outer Diameter OD

1.313 in

Bore Tolerance

+.001 in / -.000 in

Length L

1.688 in

Hub Width LH

0.590 in

Fastening Hardware

Forged Clamp Screw


Screw Material

Alloy Steel

Hex Wrench Size

2.5 mm

Screw Finish

Black Oxide

Seating Torque

2.1 Nm

Number of Screws

2 ea

Performance Specifications

Static Torque

120 lb-in

Angular Misalignment


Dynamic Torque Non-Reversing

60 lb-in

Parallel Misalignment

0.006 in

Dynamic Torque Reversing

30 lb-in

Axial Motion

0.016 in

Torsional Stiffness

400 lb-in/Deg

Maximum Speed

10,000 RPM

Additional Information

Material Specification

Hubs: 2024-T351 Aluminum Bar
Bellows: Type 321 Stainless Steel


-40°F to 200°F
-40°C to 93°C

Finish Specification

Sulfuric Anodized MIL-A-8625 Type II, Class 2 and ASTM B580 Type B Black Anodize


Ruland Manufacturing

Country of Origin


Weight (lbs.)




Product Notes

Note 1

Stainless steel hubs are available upon request.

Note 2

Torque ratings are at maximum misalignment.

Note 3

Performance ratings are for guidance only. The user must determine suitability for a particular application.

Note 4

Torque ratings for the couplings are based on the physical limitations/failure point of the metal bellows. Under normal/typical conditions the hubs are capable of holding up to the rated torque of the metal bellows. Please consult technical support for more assistance.

Prop 65

WARNING This product can expose you to chemicals including Ethylene Thiourea and Nickel (metallic), known to the State of California to cause cancer, and Bisphenol A and Ethylene Thiourea, known to the State of California to cause birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.

ISO 9001:2015


Conflict Minerals






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