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When a rigid coupling transmits every vibration and misalignment straight into your spindle or lead screw, your print quality and machining accuracy suffer. The D40 Flexible Plum Coupling Shaft Coupler is engineered for hobbyists, makers, and workshop professionals who demand smooth, reliable power transmission between stepper motors and driven shafts — without the noise and wear that rigid couplings introduce.
Each coupler consists of two precision-machined aluminum hubs and a polyurethane spider insert (plum element). The outer diameter is 40 mm (≈1.57 in), available in two body lengths: L66 mm (≈2.60 in) and L78 mm (≈3.07 in). Bore combinations range from 6 mm up to 22 mm on both the drive and driven sides, covering the most common stepper motor shaft and lead-screw diameters used in CNC routers, laser engravers, and FDM 3D printers.
Typical applications include connecting NEMA 17 / NEMA 23 stepper motor shafts to T8 or T12 lead screws in 3D printer Z-axis assemblies, coupling servo motors to ball screws in DIY CNC milling machines, and joining mismatched shaft diameters in small automation and robotics projects where angular or parallel misalignment compensation is needed.
Both drive and driven hubs are machined from aluminum alloy, keeping rotating mass low while maintaining the structural rigidity needed for accurate torque transmission.
The six-lobe plum (jaw) element absorbs angular, parallel, and axial misalignment, dampening vibration before it reaches your linear rails or print bed — extending bearing and lead-screw life.
Available in dozens of bore combinations (d1 × d2) from 6 mm × 6 mm up to 22 mm × 22 mm, so you can match virtually any stepper shaft and lead-screw pairing without adapters.
Choose the 66 mm length for compact motor mounts or the 78 mm version when you need extra clearance between motor face and driven component — both share the same 40 mm outer diameter.
Each hub is secured to its shaft with a radial set screw, providing a firm, slip-resistant grip without requiring keyways or press-fit tooling — easy to install and re-position.
Accommodates angular misalignment up to approximately 1°–3° and parallel offset up to approximately 0.2–0.5 mm, protecting your motor bearings and frame from stress caused by imperfect shaft alignment.
| Coupling Type | Flexible Jaw (Plum / Spider) |
|---|---|
| Outer Diameter (D) | 40 mm (≈1.57 in) |
| Body Length (L) | 66 mm (≈2.60 in) or 78 mm (≈3.07 in) — see variant options |
| Bore d1 (Drive Side) | 6 mm – 22 mm — see variant options |
| Bore d2 (Driven Side) | 6 mm – 22 mm — see variant options |
| Hub Material | Aluminum Alloy |
| Spider Insert Material | Polyurethane (PU) |
| Clamping Method | Set Screw |
| Angular Misalignment | Typically 1°–3° |
| Parallel Misalignment | Typically 0.2–0.5 mm |
| Finish | Natural / Anodized Aluminum |
| Quantity per Order | 1 piece |
Measure the outer diameter of your motor shaft (d1) and the outer diameter of your lead screw or driven shaft (d2) with a caliper. Select the variant whose d1 × d2 matches those measurements. If both shafts are the same diameter, choose a symmetric bore such as 8 mm × 8 mm. Common NEMA 17 motor shafts are 5 mm or 6.35 mm (¼ in); T8 lead screws are typically 8 mm.
Both lengths share the same 40 mm outer diameter and bore options. The L66 (66 mm) version is more compact and suits tight motor-mount enclosures. The L78 (78 mm) version provides extra axial clearance between the motor face and the driven component, which can be useful when the motor shaft protrudes further or when you need more room for the spider insert to flex.
The polyurethane spider insert typically accommodates angular misalignment of approximately 1°–3° and parallel (radial) offset of approximately 0.2–0.5 mm. For best results and longest spider life, align shafts as closely as possible during installation and treat the coupling's misalignment capacity as a tolerance buffer rather than a design target.
Yes. The two aluminum hubs separate once the set screws are loosened, allowing you to slide out the worn spider element and press in a new one without removing the hubs from the shafts. This makes maintenance straightforward and cost-effective over the life of the machine.
Most NEMA 17 motors have a 5 mm shaft. If your motor has a 5 mm shaft, select a variant with d1 = 5 mm. If your motor has a 6.35 mm (¼ in) shaft — common on some higher-torque NEMA 17 and NEMA 23 motors — choose d1 = 6.35 mm. Always verify your motor's shaft diameter in its datasheet before ordering.
Slide each hub onto its respective shaft until the shaft end is flush with or slightly recessed from the outer face of the hub. Tighten the set screw firmly against the shaft flat (if present) or against the shaft surface. Insert the spider element between the two hubs, then bring the hubs together so the spider lobes seat fully in the hub slots. Verify shaft alignment before final tightening.
The hubs are machined from aluminum alloy with a natural or lightly anodized finish. This provides adequate corrosion resistance for indoor workshop and 3D-printer environments. For high-humidity or outdoor applications, consider applying a light coat of machine oil to exposed surfaces.
