GM series helical beam coupling machined from a single piece of anodised aluminium alloy with a continuous spiral cut. The spiral gives more flexibility than a straight slit design, so it forgives angular and parallel misalignment easily while staying completely free of backlash, with nothing to wear out. Light aluminium construction keeps the inertia low, which suits encoders and small fast-reversing motors. Fourteen sizes, outer diameters 12 to 50 mm, bores 3 to 32 mm, including the imperial-derived diameters used on many small motors.
Technical specifications
| Series | GM |
|---|---|
| Coupling type | Helical (spiral cut) beam coupling, single piece |
| Material | Aluminium alloy |
| Surface treatment | Anodised |
| Shaft attachment | Set screw (grub screw) on each hub |
| Outer diameter range | 12 mm to 50 mm |
| Bore range | 3 mm to 32 mm depending on size |
| Backlash | Zero, one-piece construction |
| Wearing parts | None |
| Misalignment | Angular, parallel and axial; more forgiving than a parallel slit beam |
| Brand and origin | GND / Guangzhida, Dongguan, China |
| Typical applications | Encoders, micro motors, small lead screws, light stepper axes, laboratory and instrument drives |
Available sizes
Each size is ordered with the two bore diameters you need, one for the motor shaft and one for the driven shaft.
| Size (outer diameter x length) | Bore range |
|---|---|
| 12 x 18.5 mm | 3 to 6.35 mm |
| 15.5 x 21 mm | 4 to 6.35 mm |
| 15.5 x 23 mm | 4 to 6.35 mm |
| 17.5 x 23 mm | 4 to 8 mm |
| 19.1 x 19.1 mm | 5 to 10 mm |
| 19.5 x 24.5 mm | 5 to 10 mm |
| 25 x 31 mm | 6 to 12 mm |
| 25.4 x 25.4 mm | 6 to 12.7 mm |
| 28.6 x 28.6 mm | 8 to 14 mm |
| 32 x 32 mm | 8 to 18 mm |
| 32 x 41 mm | 8 to 18 mm |
| 38.1 x 38.1 mm | 8 to 22 mm |
| 42 x 50 mm | 12 to 28 mm |
| 50 x 50 mm | 12 to 32 mm |
How to order
Couplings are quoted per order, with no price shown on the site. Send us the series GM, the outer diameter and length you need, and the two bore diameters, for example GM-25X31 with 8 mm and 10 mm bores. If you do not know which size fits, send the motor shaft diameter, the driven shaft diameter, the torque and the space available between the two shafts, and our engineers select it for you. RendatSP ships to Saudi Arabia, Iraq, the UAE, Egypt, Oman, Libya, Morocco, Mauritania, Yemen, Algeria, Jordan and Syria.
Frequently asked questions
Spiral cut or parallel slit, which should I use?
A spiral cut flexes more, so it takes larger misalignment and puts less load on small bearings. A parallel slit is torsionally stiffer and better where the drive has to hold position tightly. For encoders and light axes the spiral is usually the right choice.
Why are some sizes 19.1, 25.4 and 38.1 mm?
Those are the metric equivalents of 0.75, 1.0 and 1.5 inch, kept because many small motors and imperial machine builds use them. Bores of 6.35 mm and 12.7 mm, that is 1/4 inch and 1/2 inch, are available for the same reason.
Does the set screw damage the shaft?
It leaves a small mark where it seats, which is normal for this type. If you need the shaft left untouched, or the drive reverses constantly, use a clamp type coupling instead and we will quote the equivalent size.
How much torque will it carry?
Torque rises with the outer diameter, and an aluminium spiral beam carries less than a stainless one of the same size. Tell us the motor torque and the size you are looking at and we confirm it before you order.
Can it be used in a washdown area?
Not the aluminium version. For wet or corrosive environments use the stainless steel beam coupling, which we also supply.
