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When shaft misalignment or vibration disrupts your CNC router, stepper motor drive, or 3D printer axis, the weak link is almost always the coupling. Engineers and makers who demand repeatable positioning accuracy need a flexible plum jaw shaft coupler that absorbs angular, parallel, and axial misalignment without transmitting shock loads back into bearings or encoders. The D40 Flexible Plum Coupling Shaft Coupler is engineered for exactly that role, fitting a wide range of motor-to-leadscrew connections across hobby and light-industrial builds.
Each coupler consists of two aluminum alloy hubs (outer diameter 40 mm / 1.57 in) and a polyurethane spider insert (plum jaw). The overall body length is either 50 mm (≈ 1.97 in) for the L50 variant or 55 mm (≈ 2.17 in) for the L55 variant. Bore diameters (d1 × d2) span 6 mm through 22 mm on both sides, covering metric and fractional inch shaft sizes including 6.35 mm (¼ in) and 12.7 mm (½ in). Set screws secure each hub independently, allowing different bore sizes on each end.
Typical applications include CNC stepper motor to ball-screw or lead-screw connections, 3D printer Z-axis motor couplings, laser engraver drive shafts, and light servo-to-shaft connections in automation rigs. The flexible plum jaw shaft coupler design is a go-to solution for DIY CNC stepper motor coupling upgrades and 3D printer Z-axis coupler replacements where rigid couplings cause layer-shift artifacts.
| Outer Diameter (D) | 40 mm (1.57 in) |
|---|---|
| Body Length (L) | 50 mm (1.97 in) or 55 mm (2.17 in) — see variant options |
| Bore Diameter d1 × d2 | 6–22 mm (including 6.35 mm & 12.7 mm) — see variant options |
| Hub Material | Aluminum alloy |
| Spider / Insert Material | Polyurethane (PU) |
| Clamping Method | Set screw (per hub) |
| Misalignment Tolerance | See variant options |
| Max Torque | See variant options |
| Finish | Natural anodized aluminum |
| Quantity per Order | 1 piece |
Measure the shaft diameter of your motor (d1) and the shaft diameter of your lead screw or ball screw (d2) with a caliper. Select the variant that matches both values exactly. If your shafts are the same diameter, choose a symmetric option such as 8 mm × 8 mm. If they differ, choose the asymmetric option, for example 8 mm × 10 mm. Fractional inch shafts like ¼ in (6.35 mm) and ½ in (12.7 mm) are available as dedicated variants.
Choose L50 (50 mm) when motor-to-screw clearance is tight or when you want a stiffer feel with less spider compression travel. Choose L55 (55 mm) when you need slightly more axial float or when your frame geometry requires the extra 5 mm of body length. Both lengths share the same D40 outer diameter and bore range.
The aluminum alloy hubs provide rigid torque transmission between the set screws and the spider lobes. The polyurethane spider insert handles misalignment and vibration damping. For typical NEMA 17 and NEMA 23 stepper motor applications in CNC routing and 3D printing, the D40 plum coupler is well within the torque range of these motors. For exact torque ratings, contact us to confirm.
The aluminum alloy hubs have a natural anodized finish that provides moderate corrosion resistance suitable for indoor workshop and enclosed machine environments. The polyurethane spider is resistant to oils and mild chemicals. For prolonged outdoor or high-humidity exposure, consider applying a light protective coating to the hubs.
NEMA 17 motors typically have a 5 mm shaft. NEMA 23 motors commonly use 6.35 mm (¼ in) or 8 mm shafts. This coupler's bore range starts at 6 mm, so it covers NEMA 23 and larger motors directly. For a 5 mm NEMA 17 shaft, a 5 mm bore variant is not in this D40 series — please check our other coupler listings or contact us for guidance.
Yes. Replacing a rigid coupling with a flexible plum jaw coupler on the Z-axis is a common upgrade that reduces Z-wobble artifacts caused by motor shaft and lead screw misalignment. The D40 outer diameter fits most standard 3D printer coupler pockets. Confirm your motor shaft and lead screw diameters, then select the matching bore variant.
Insert each shaft fully into its respective hub bore. Align the set screw with a flat on the shaft if one is present, or position it over the shaft surface. Tighten the set screw with the appropriate hex key (typically M3 or M4) to the manufacturer's recommended torque — finger-tight plus a quarter turn is a common starting point for small CNC applications. Do not overtighten, as this can deform the bore. Re-check tightness after the first few hours of operation.
