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Rigid couplings transmit every vibration and misalignment shock directly into motor bearings and lead screws, shortening machine life and degrading positioning accuracy. CNC builders, robotics integrators, and servo drive engineers who need a forgiving connection between motor and driven shaft rely on flexible plum shaft couplers to absorb angular and parallel offset without sacrificing torque transmission or introducing backlash.
Each coupler consists of two aluminum alloy hubs and a polyurethane spider (plum) insert that sits between the jaw faces. Available in three body sizes — D30 mm × L35 mm, D30 mm × L42 mm, and D35 mm × L50 mm (≈1.18–1.38 in OD, 1.38–1.97 in length) — with shaft bore options spanning 5 mm to 19 mm (≈0.20–0.75 in), covering same-diameter and stepped-bore configurations. Multi-pack options of 1, 3, 5, 7, or 10 pieces are available.
Typical applications include CNC router and laser engraver axis drives where flexible plum coupling for stepper motor installations reduces resonance and lost steps, servo motor test benches requiring low-backlash torque transmission, and light-duty robotic joint connections where the elastomer insert provides a degree of shock absorption between drive and load.
The elastomer plum insert sits between the two aluminum jaw hubs, absorbing angular misalignment of typically 1–3° and parallel offset of typically 0.1–0.3 mm while dampening vibration that would otherwise reach motor bearings.
Bore options from 5 mm to 19 mm (≈0.20–0.75 in) include same-diameter pairs and stepped configurations (e.g., 5 mm × 16 mm, 8 mm × 19 mm), making these suitable for motor-to-lead-screw connections with different shaft diameters on each end.
Each aluminum hub is secured to its shaft via set screws, providing positive grip on both round and D-cut shafts without requiring keyways or adhesives.
D30 mm bodies (L35 mm and L42 mm) suit compact NEMA 17 and small servo applications; the D35 mm × L50 mm body handles higher-torque NEMA 23 and mid-frame servo drives. Select the size that fits your motor mount clearance.
Order 1, 3, 5, 7, or 10 pieces per SKU — ideal for multi-axis machine builds, workshop stock, or replacing worn spider inserts across a machine fleet.
OD and length dimensions match common aftermarket plum coupler footprints, allowing direct replacement of worn or rigid couplings on most CNC and servo drive frames without machining.
| Coupler Type | Flexible jaw (plum/spider) coupler |
|---|---|
| Hub Material | Aluminum alloy |
| Insert Material | Polyurethane elastomer (spider) |
| Outer Diameter (OD) | D30 mm (≈1.18 in) / D35 mm (≈1.38 in) |
| Overall Length | 35 mm / 42 mm / 50 mm (≈1.38–1.97 in) |
| Shaft Bore Diameter | See variant options (5 mm–19 mm) |
| Bore Configuration | Same-diameter or stepped (see variant options) |
| Angular Misalignment Tolerance | Typically 1–3° |
| Parallel Offset Tolerance | Typically 0.1–0.3 mm |
| Clamping Method | Set screw (both hubs) |
| Finish | Natural anodized aluminum |
| Pack Quantity | See variant options (1 / 3 / 5 / 7 / 10 pcs) |
| Weight (per unit) | See variant options |
The D30 mm body (L35 mm or L42 mm) is sized for compact NEMA 17 stepper motors and small servo frames where radial clearance is limited. The D35 mm × L50 mm body suits NEMA 23 steppers and mid-frame servo motors that produce higher torque. Match the coupler OD to the clearance available in your motor mount bracket.
A plum coupler uses two aluminum hubs with interlocking jaws and a separate polyurethane spider insert between them. This design provides zero-backlash torque transmission and good vibration damping, but the spider insert is a wear item that can be replaced independently. A helical coupler is a single-piece machined body with a spiral cut — it has no wear parts but offers less vibration damping. Plum couplers are generally preferred for servo drives; helical couplers are common in 3D printer Z-axis applications.
Yes. Stepped-bore variants (e.g., 5 mm × 16 mm or 8 mm × 19 mm) are designed exactly for this purpose — one bore end accepts the motor shaft, the other accepts the lead screw or driven shaft. Confirm both diameters before ordering by measuring your motor shaft and lead screw OD.
The polyurethane spider insert typically accommodates angular misalignment of 1–3° and parallel (radial) offset of 0.1–0.3 mm. These are conservative estimates for standard jaw couplers of this size. Minimizing misalignment at installation extends spider insert life and reduces heat buildup in the elastomer.
Yes. The spider insert sits between the two hub jaws and can be removed and replaced without disassembling the motor or driven shaft. Ordering a multi-pack gives you spare inserts and hubs for future maintenance, which is particularly useful in multi-axis machines where all axes use the same coupler size.
Yes. The set-screw clamping design works with both round and D-cut shafts. For D-cut shafts, orient one set screw to bear against the flat face for maximum grip and to prevent rotation under load.
Multi-axis CNC machines typically require one coupler per axis (X, Y, Z), so a 3-pack covers a full 3-axis build. The 5-, 7-, and 10-packs are cost-effective for workshop stock, machine fleet maintenance, or builds with multiple driven axes. Per-unit cost decreases with larger pack sizes.
