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When a rigid coupler transmits every vibration and angular error directly into your motor bearings, precision suffers and components wear prematurely. Makers, CNC builders, and automation engineers who need a forgiving connection between two shafts rely on a flexible jaw-style coupling to absorb the shock. This plum (spider-jaw) shaft coupler is designed for exactly that role, bridging two shafts of different or equal diameters without sacrificing rotational accuracy.
Each coupler consists of two aluminium alloy hubs and a polyurethane spider insert. The outer diameter is 40 mm (approx. 1.57 in) and the overall length is either 55 mm (approx. 2.17 in) or 66 mm (approx. 2.60 in) depending on the variant selected. Bore combinations range from 6 mm up to 22 mm (approx. 0.24 in – 0.87 in), including imperial-friendly 6.35 mm (1/4 in) and 12.7 mm (1/2 in) options, covering the most common stepper motor and lead-screw shaft sizes.
Typical applications include CNC router Z-axis lead-screw connections, 3D printer Z-axis flexible coupling replacements, stepper motor to ball-screw shaft adapters, and light-duty servo drive train assemblies where parallel or angular misalignment compensation is needed.
Accepts shaft diameters from 6 mm to 22 mm on each hub independently, including 6.35 mm (1/4") and 12.7 mm (1/2") imperial sizes — one listing covers dozens of motor-to-screw combinations.
The polyurethane jaw insert absorbs torsional shock, dampens vibration, and compensates for up to ±1° angular and ~0.2 mm parallel misalignment without transmitting load spikes to motor bearings.
Both hubs are machined from aluminium alloy for a lightweight yet rigid grip. Each hub is secured to its shaft via a radial set screw, providing a firm, slip-resistant connection under continuous rotation.
Choose D40 × L55 mm for compact installations or D40 × L66 mm where additional spider clearance or shaft engagement length is needed — both share the same bore range and outer diameter.
Standard D40 outer diameter matches widely available coupler mounts and motor brackets. Swap a worn rigid coupler or upgrade from a solid coupler on your CNC Z-axis in minutes.
Radial hex set screws on each hub lock the coupler firmly to both shafts. Use a standard hex key (Allen wrench) for installation — no special tooling required.
| Coupling Type | Flexible jaw / plum spider |
|---|---|
| Outer Diameter (D) | 40 mm (1.57 in) |
| Overall Length (L) | 55 mm (2.17 in) or 66 mm (2.60 in) — see variant options |
| Bore d1 (Motor Side) | 6 – 22 mm (see variant options) |
| Bore d2 (Screw Side) | 6 – 22 mm (see variant options) |
| Hub Material | Aluminium alloy |
| Spider Insert Material | Polyurethane (PU) |
| Shaft Retention | Radial set screw (hex key) |
| Misalignment Tolerance | Angular: typically ±1°; Parallel: typically ≤0.2 mm |
| Finish | Natural anodised aluminium |
| Quantity per Order | 1 piece |
Measure the diameter of each shaft you need to connect. d1 is the bore for the motor-side shaft and d2 is the bore for the lead-screw or ball-screw side. Select the variant that matches both diameters exactly — for example, "8mm to 10mm" means one hub bores 8 mm and the other bores 10 mm. If both shafts are the same size, choose the equal-bore option such as "8mm to 8mm".
NEMA 17 stepper motors typically have a 5 mm output shaft. This listing starts at 6 mm bore, so it does not cover 5 mm shafts. For NEMA 17 with a 5 mm shaft paired with a 6 mm or 8 mm lead screw, you would need a 5 mm bore option. NEMA 23 motors commonly use 6.35 mm (1/4") or 8 mm shafts, both of which are available in this listing.
Both lengths share the same 40 mm outer diameter and bore range. The L55 mm version is more compact and suits tight motor-to-screw clearances. The L66 mm version provides a longer spider engagement zone, which can improve vibration damping and is useful when the shaft insertion depth needs to be greater on one or both sides.
The polyurethane spider insert typically accommodates angular misalignment of up to approximately ±1° and parallel (radial) misalignment of up to approximately 0.2 mm. For best results and longest spider life, align shafts as closely as possible during installation and use the coupler to absorb residual misalignment rather than as a primary alignment correction device.
Yes. The two aluminium hubs separate to expose the spider insert. Standard D40 plum spider inserts are widely available as spare parts. When the insert shows visible cracking, deformation, or the coupler develops noticeable backlash, replace the insert rather than the entire coupler assembly.
The hubs use standard metric hex (Allen) set screws. The exact hex key size depends on the bore diameter of the hub — smaller bores typically use M3 or M4 set screws (2 mm or 2.5 mm hex key) while larger bores may use M5 (2.5 mm or 3 mm hex key). A standard hex key set covers all sizes. Tighten firmly but avoid over-torquing on aluminium threads.
This coupler is designed for low-to-medium speed CNC and automation applications such as lead-screw drives and stepper motor connections, typically up to a few hundred RPM. For high-speed spindle or servo applications requiring precise torque transmission and minimal backlash at elevated RPM, a bellows or disc-type coupler is generally more appropriate.
