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When a stripped or undersized gear brings your machine to a halt, the cost isn't just the part — it's the downtime. Engineers, fabricators, and serious DIYers who build CNC routers, robotic arms, conveyor systems, and custom gearboxes need spur gears that hold their tooth profile under load, cycle after cycle. These 45# steel spur gears are machined to deliver consistent mesh engagement across a wide range of module and tooth-count combinations.
Each gear is machined from 45# medium-carbon steel, offering a tensile strength typically in the range of 600–800 MPa before any additional heat treatment. Available in Modulus 3, 4, or 5, with tooth counts from 10T to 32T, and face widths of 30mm (~1.18 in), 35mm (~1.38 in), or 40mm (~1.57 in). The bore diameter and pitch circle diameter vary by module and tooth count — see variant options for your specific combination.
These spur gears suit three common scenarios: replacing worn pinion gears in industrial conveyor drives, building custom reduction stages for electric motor projects, and assembling precision axis drives in hobbyist CNC and 3D-printer gantry systems. The standardized module sizing means they mesh directly with any same-module rack or mating gear without custom modification.
45# Medium-Carbon Steel Construction — Machined from 45# steel for a balance of machinability and load-bearing strength, suitable for moderate-to-heavy duty power transmission without the brittleness of cast iron alternatives.
Three Module Options (Mod 3 / 4 / 5) — Covers the most common metric module standards used in industrial and hobbyist machinery, allowing direct drop-in replacement or new-build compatibility with standard racks and mating gears.
Wide Tooth-Count Range (10T – 32T) — Select the exact tooth count needed to achieve your target gear ratio without resorting to custom machining. Finer ratios are achievable by pairing different tooth counts within the same module.
Three Face Width Choices (30 / 35 / 40mm) — A wider face distributes tooth load over a greater contact area, reducing surface stress. Choose 30mm for space-constrained assemblies, 40mm where torque capacity is the priority.
Standard Involute Tooth Profile — The involute form maintains a constant velocity ratio throughout mesh engagement, minimizing vibration and noise in continuous-duty applications such as motor drives and automated equipment.
Bore Ready for Keyway or Set-Screw Fitment — The through-bore is sized to accept standard shaft diameters for the given module; confirm bore diameter from the variant specifications or contact us to confirm fitment for your shaft size.
| Material | 45# Medium-Carbon Steel |
|---|---|
| Available Modulus | Mod 3, Mod 4, Mod 5 |
| Tooth Count Range | 10T – 32T (select by variant) |
| Face Width Options | 30mm (1.18 in) / 35mm (1.38 in) / 40mm (1.57 in) |
| Tooth Profile | Standard Involute (metric module) |
| Pressure Angle | 20° (standard) |
| Bore Diameter | See variant options |
| Pitch Circle Diameter | See variant options (= Module × Tooth Count) |
| Surface Finish | Machined; natural steel (untreated unless specified) |
| Gear Type | External Spur Gear (Pinion) |
| Mounting | Through-bore; keyway or set-screw fitment |
| Weight | See variant options |
Measure the outside diameter (OD) of your existing gear in millimeters, then count the number of teeth. Use the formula: Module = OD ÷ (Tooth Count + 2). For example, a gear with an OD of 36mm and 16 teeth gives Module = 36 ÷ 18 = 2 — meaning you would need a Mod 2 gear. If your result is close to 3, 4, or 5, one of these variants will be a direct match.
No. Gears of different modules are not interchangeable and will not mesh correctly. The module defines the tooth size — a Mod 3 gear must pair with another Mod 3 gear or a Mod 3 rack. Mixing modules causes improper engagement, accelerated wear, and potential gear failure.
Face width affects how much load the gear can carry. A 30mm face is suitable for lighter-duty or space-constrained applications. A 35mm face is a balanced choice for general-purpose drives. A 40mm face provides the greatest tooth contact area and is recommended when transmitting higher torque or operating under sustained load. If in doubt, choose the widest face that fits your housing.
45# steel in its as-machined state has a tensile strength typically in the range of 600–800 MPa, which is adequate for moderate-duty power transmission, robotics, CNC axis drives, and conveyor systems running at normal speeds and loads. For very high-speed, high-shock, or continuous heavy-load applications, you may want to consider surface hardening (induction hardening or case hardening) after purchase, or contact us to discuss your specific load requirements.
45# carbon steel is not stainless and will oxidize when exposed to moisture without protection. For outdoor or high-humidity use, apply a gear lubricant, grease, or a rust-inhibiting coating after installation. Regular re-lubrication will significantly extend service life in exposed environments.
Gear ratio = Driven Gear Tooth Count ÷ Driver Gear Tooth Count. For example, pairing a 10T driver with a 30T driven gear gives a 3:1 reduction ratio — the output shaft turns once for every three turns of the input shaft. Both gears must be the same module to mesh correctly. You can combine any two tooth counts from the 10T–32T range within the same module to achieve ratios from approximately 1:1 up to 3.2:1 in a single stage.
The standard bore diameter varies by module — contact us to confirm the exact bore for your selected Modulus and tooth count before ordering. The 45# steel construction is machinable, so a qualified machine shop can re-bore or broach a keyway if the standard bore does not match your shaft. Do not force-fit a shaft larger than the bore, as this can crack the hub.
