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When misalignment between motor and drive shaft causes vibration, noise, or premature wear, the right universal flexible shaft coupling coupler makes all the difference. Designed for RC boat builders, robotics enthusiasts, and mechanical DIYers who need reliable torque transmission across slight angular or parallel offsets, this U-joint connector eliminates the frustration of rigid couplings that crack under load.
Each coupler is machined from steel and features a flexible universal joint design. Inner diameter (I.D.) options range from 6 mm to 20 mm (approx. 0.24″–0.79″), outer diameter (O.D.) from 16 mm to 32 mm (approx. 0.63″–1.26″), and overall length from 42 mm to 85 mm (approx. 1.65″–3.35″). Set screws secure the coupler firmly to both shafts. Available in 1PCS or 2PCS packing quantities.
Typical applications include RC boat motor-to-propeller shaft connections, small CNC machine spindle couplings, DIY electric vehicle drive trains, and benchtop lathe or drill press shaft adapters — anywhere a flexible shaft coupling for motor is needed to absorb minor misalignment without sacrificing torque.
| Product Type | Universal Flexible Shaft Coupling / U-Joint Coupler |
|---|---|
| Material | Steel |
| Inner Diameter (I.D.) Range | 6 mm – 20 mm (0.24″ – 0.79″) |
| Outer Diameter (O.D.) Range | 16 mm – 32 mm (0.63″ – 1.26″) |
| Length Range | 42 mm – 85 mm (1.65″ – 3.35″) |
| Available Sizes (I.D. × O.D. × L) | 6×16×42 / 8×16×42 / 10×20×45 / 12×24×51 / 12×25×56 / 14×28×60 / 14×28×70 / 15×32×85 / 16×32×85 / 18×32×85 / 20×32×85 mm |
| Shaft Fixing Method | Set screw (both ends) |
| Packing Quantity | 1PCS or 2PCS (see variant options) |
| Finish | See variant options |
| Max Recommended RPM | Contact us to confirm |
| Max Torque Rating | Contact us to confirm |
| Application | RC boats, motors, CNC spindles, DIY drive systems |
Measure the outer diameter of both shafts you need to connect — this is your required I.D. (inner diameter). Then select the variant whose I.D. matches your shaft size. For example, if your motor shaft is 8 mm and your drive shaft is also 8 mm, choose the 8×16×42 mm variant. If the two shafts differ in diameter, this coupler is not suitable — you would need a reducing coupler instead.
Yes. The universal joint (U-joint) design allows for a small degree of angular misalignment — typically up to a few degrees — between the input and output shafts. This makes it well-suited for RC boat installations where the motor and propeller shaft are not perfectly in line. For large misalignment angles, a dedicated CV joint or flexible jaw coupler may be more appropriate.
The steel construction provides solid torque transmission for typical RC boat motor outputs. However, maximum RPM and torque ratings depend on the specific size selected and the operating conditions. For high-performance or competition RC applications, please contact us to confirm suitability before ordering.
The coupler is made from steel. While steel offers good mechanical strength, it can be susceptible to surface oxidation in prolonged wet or saltwater environments. For RC boat use, we recommend applying a light coat of waterproof grease or corrosion inhibitor to the coupler after installation, and rinsing with fresh water after saltwater use.
Installation requires only a hex key (Allen wrench) to tighten the set screws on each end of the coupler. Slide the coupler onto both shafts, align to your desired position, then tighten the set screws firmly. No adhesive, press-fit tools, or special equipment are needed for standard installations.
Both options contain the same coupler in the same size. The 1PCS option is ideal if you need a single replacement or are testing a size for the first time. The 2PCS option provides a spare unit at a better per-piece value — useful for workshop stock, multi-boat builds, or projects where having a backup on hand saves downtime.
No — this coupler has the same I.D. on both ends, so it is designed for shafts of equal diameter. If you need to connect shafts of different diameters, please contact us or browse our range of reducing shaft couplers.
