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When your CNC router, robotic arm, or motorized drive system demands low-noise, vibration-reduced power transfer, standard spur gears often fall short. Engineers and makers who need reliable torque transmission with gradual tooth engagement turn to left-spiral helical gears — and this range covers the most common modulus and tooth-count combinations in a single listing.
These helical gears are machined from steel and feature a step/keyway bore design for secure shaft mounting. Available in 1.5 modulus (13, 15, 20, 26, and 30 teeth) and 2 modulus (15 teeth), with bore diameters ranging from 10 mm (~0.39 in) to 25 mm (~0.98 in). Keyway dimensions scale with bore size: 4×2 mm, 5×2.5 mm, 6×3 mm, or 8×3.5 mm, ensuring a positive key fit without slippage.
Typical applications include CNC machine Z-axis drives, stepper and servo motor gearboxes, conveyor reduction stages, and DIY automation projects requiring left-hand helix pairing with a matching right-spiral counterpart. The stepped bore profile also suits shaft-collar assemblies where axial positioning is critical.
| Modulus | 1.5 / 2 (see variant options) |
|---|---|
| Tooth Count | 13T, 15T, 20T, 26T, 30T (1.5M); 15T (2M) |
| Helix Direction | Left spiral |
| Pressure Angle | 20° (standard metric) |
| Bore Diameter | 10 / 12 / 14 / 15 / 16 / 17 / 18 / 19 / 20 / 22 / 24 / 25 mm |
| Keyway Dimensions | 4×2 mm / 5×2.5 mm / 6×3 mm / 8×3.5 mm (matched to bore) |
| Material | Steel |
| Bore Type | Step bore with keyway |
| Quantity per Pack | 1 pc |
| Outer Diameter | See variant options |
| Face Width | See variant options |
| Weight | See variant options |
Modulus determines the size of each tooth — a higher modulus means larger, stronger teeth suited for higher torque. For light-duty CNC or robotics, 1.5 modulus is common. For heavier loads or larger shaft diameters, 2 modulus provides more tooth strength. Tooth count, combined with the mating gear's tooth count, sets your gear ratio. Divide the driven gear teeth by the driving gear teeth to get the ratio.
Match the bore diameter to your shaft's outer diameter. The keyway dimensions are pre-matched to the bore in each variant (e.g., a 10 mm or 12 mm bore uses a 4×2 mm keyway; a 24–25 mm bore uses an 8×3.5 mm keyway). Measure your shaft carefully and confirm the keyway slot on your shaft matches the listed keyway size before ordering.
Helical gears must be paired with a mating gear of the same modulus and complementary helix direction. A left-spiral gear meshes with a right-spiral gear on parallel shafts. Using two left-spiral gears together on parallel shafts is not correct and will result in improper meshing. Confirm your mating gear's helix direction before purchasing.
These steel helical gears are suited for moderate-load, moderate-speed motor transmission applications typical in CNC machines, robotics, and DIY automation. Exact load ratings depend on operating speed, lubrication, and center distance accuracy. For heavy industrial duty cycles with continuous high torque, consult a gear engineer to verify suitability.
These gears are machined from steel and do not include a corrosion-resistant coating unless otherwise specified. For environments with moisture or mild chemicals, applying a light machine oil or grease during installation will help protect the tooth surfaces. For highly corrosive environments, consider stainless steel or coated alternatives.
A step bore features a shoulder inside the bore that allows the gear to be positioned axially on a shaft at a defined depth, which is useful when precise axial location is needed. Combined with the keyway, it provides both rotational and axial retention. A standard through bore has no shoulder and relies entirely on set screws or collars for axial positioning.
Yes, lubrication is recommended for all steel helical gear applications to reduce wear and heat buildup. Apply a suitable gear grease or machine oil to the tooth faces at installation. For enclosed gearboxes, an oil bath is ideal. For open drives, periodic re-greasing based on operating hours and environment is advised.
