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Ruland MBC51-20-14-A, 20mm x 14mm Bellows Coupling, High Stiffness, Aluminum, 50.8mm, OD 61.3mm Length

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Ruland MBC51-20-14-A is a high stiffness bellows coupling with 20mm x 14mm bores, 50.8mm OD, and 61.3mm length. It has fewer convolutions than comparably sized increased misalignment styles allowing for increased torsional stiffness making it the ideal choice for precision positioning applications. MBC51-20-14-A is comprised of two anodized aluminum hubs and a stainless steel bellows for lightweight and low inertia. It is also engineered with a balanced design for reduced vibration at high speeds up to 10,000 RPM. The thin walls of the bellows are able to flex while remaining rigid under torsional loads allowing for the accommodation of all forms of misalignment. Hardware is metric and tests beyond DIN 912 12.9 standards for maximum torque capabilities. MBC51-20-14-A is machined from meticulously selected bar stock that is sourced exclusively from North American mills. It is carefully made in our ISO 9001:2015 advanced manufacturing facility in Marlborough, MA under strict controls using proprietary processes. MBC51-20-14-A is RoHS3, REACH, and Conflict Minerals compliant.



Bore (B1) Larger inner diameter. Should match nominal shaft diameter.

20 mm

Small Bore (B2) Smaller inner diameter. Should match nominal shaft diameter.

14 mm

B1 Max Shaft Penetration The maximum depth the shaft can penetrate into Bore B1.

27.9 mm

B2 Max Shaft Penetration The maximum depth the shaft can penetrate into Bore B2.

27.9 mm

Outer Diameter (OD)

50.8 mm

Bore Tolerance Variance in finished bore range before installation.

+0.03 mm / -0.00 mm

Length (L)

61.3 mm

Length Tolerance

+/- 0.76 mm

Hub Width (LH)

20.55 mm

Recommended Shaft Tolerance Acceptable variance in nominal shaft diameter before performance loss.

+0.000 mm / -0.013 mm

Fastening Hardware

Forged Clamp Screw Inch or metric socket head cap screw size.


Screw Material

Alloy Steel

Hex Wrench Size Wrench size that fits the screw head to tighten or loosen the screw.

4.0 mm

Screw Finish Surface finish and treatments on supplied hardware.

Black Oxide

Seating Torque Torque required to install supplied hardware. Use torque wrench for accurate seating torque.

9.5 Nm

Number of Screws

2 ea

Peformance Specifications

Dynamic Torque Reversing Max torque when coupling reverses direction without stopping.

11.30 Nm

Angular Misalignment Max angle of the shaft axes relative to each other.


Dynamic Torque Non-Reversing Max torque for the coupling during quick changes in acceleration or deceleration.

22.60 Nm

Parallel Misalignment Shafts are parallel to each other, but not in-line with each other. They are offset.

0.25 mm

Static Torque Unidirectional constant max torque.

45.2 Nm

Axial Motion The amount shafts can move closer to or away from each other. This is meant for thermal expansion of the shafts. No axial force can be placed on the coupling.

0.50 mm

Torsional Stiffness Measures the rigidity of the coupling. The more rigid the coupling, the less windup it will have.

108 Nm/Deg

Moment of Inertia

81.104 x10-6 kg-m2

Maximum Speed

10,000 RPM

Full Bearing Support Required? Full bearing support is a bearing in close proximity to both sides of the coupling to prevent axial loads that could result in rapid coupling failure.


Zero-Backlash? Zero-backlash ensures there is no loss of motion during operation.


Balanced Design The balanced design allows for reduced vibration at high RPMs.


Recommended Installation Tools

Torque Wrench This torque wrench and bit combo is recommended to ensure proper installation. A torque wrench prevents the screw from being over torqued which can lead to product failure.


Recommended Hex Key This hex key set has the appropriate hex key for product installation. Trained and experienced assemblers can use a hex key in place of a torque wrench.

Metric Hex Keys

Additional Information

Material Specification

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

Temperature Minimum and maximum operating temperature. Operating temperature includes ambient temperature plus or minus factors such as system heat generated during operation, washdown, vacuum, etc...

-40°F to 200°F (-40°C to 93°C)

Finish Specification Surface finish specifications.

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

Bellows Attachment Method The method used to attach the bellows to the hubs.



Ruland Manufacturing

Country of Origin


Weight (lbs)




Tariff Code


UNSPC Code used to identify products to standardize nomenclature around the world.


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. In some cases, especially when the smallest standard bores are used or where shafts are undersized, slippage on the shaft is possible below the rated torque of the metal bellows. Keyways are available to provide additional torque capacity in the shaft/hub connection when required. Please consult technical support for more assistance.

Prop 65 Required for the US State of California only.

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






Installation Instructions

  1. Align the bores of the MBC51-20-14-A bellows coupling on the shafts that are to be joined and determine if the misalignment parameters are within the limits of the coupling. (Angular Misialignment: 2.0°, Parallel Misalignment: 0.25 mm, Axial Motion: 0.50 mm)
  2. Fully tighten the M5 screw on the first hub to the recommended seating torque of 9.5 Nm using a 4.0 mm hex torque wrench.
  3. Before tightening the screw on the second hub, rotate the coupling by hand to allow it to reach its free length.
  4. Tighten the screw on the second hub to the recommended seating torque. Make sure the coupling remains axially relaxed and the misalignment angle remains centered along the length of the coupling.
  5. The shafts may extend into the relieved portion of the bore as long as it does not exceed the shaft penetration length of 27.9 mm.


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