1 Mod 21 Teeth Spur Gears (45# Steel) Transmission Motor Gear Bore 6/6.35/8mm

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1 Mod 21 Teeth Spur Gears (45# Steel) Transmission Motor Gear Bore 6/6.35/8mm

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Model: 1 Mod 21 Teeth

Bore: 6mm

Price:

$10.85 USD

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In stock (500 units), ready to be shipped

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1 Mod 21 Teeth Spur Gears — Reliable Power Transmission for DIY Automation

When your motor drive system demands precise torque transfer and consistent mesh engagement, a poorly matched gear becomes the weakest link in your build. Whether you are assembling a desktop CNC router, a robotic arm, or a custom conveyor mechanism, the 1 Mod 21 Teeth Spur Gear in 45# steel gives makers, engineers, and workshop builders a dependable transmission component that holds up under repeated load cycles.

Each gear is machined from 45# medium-carbon steel, offering a solid balance of hardness and machinability. The module is 1 (Mod 1), with 21 teeth and a standard 20° pressure angle. Bore options span 6 mm (~0.236 in), 6.35 mm (~0.250 in / 1/4 in), and 8 mm (~0.315 in), covering the most common motor shaft diameters used in hobby and light-industrial automation.

Typical use cases include DIY robotics joint drives requiring a compact 1 mod spur gear set, CNC axis transmission systems pairing a stepper motor with a 21-tooth drive gear, and small conveyor or indexing table builds where a steel motor transmission gear ensures long service life without deformation under sustained torque.

⚙️ Compatible with Mod 1 gear systems | 20° pressure angle | Pairs with 1 Mod pinions, racks, and mating gears of any tooth count

✅ Key Features of These 1 Mod 21 Teeth Spur Gears

🔩45# Steel Construction — Medium-carbon steel provides solid hardness and wear resistance for sustained transmission duty in automation and robotics applications.
📐Mod 1 / 21 Teeth Specification — Standard module 1 tooth profile ensures accurate mesh with any compatible Mod 1 mating gear, rack, or pinion in your drivetrain.
🎯Three Bore Options — Available in 6 mm, 6.35 mm (1/4 in), and 8 mm bore diameters to fit the most common stepper motor and DC motor shaft sizes without adapter sleeves.
⚡20° Pressure Angle — Industry-standard pressure angle delivers smooth, low-noise tooth engagement and efficient torque transfer across the full contact ratio.
🔧Setscrew Hub Design — Machined hub with setscrew flat allows secure shaft locking and straightforward installation on keyed or plain motor shafts.
🏗️Broad Application Range — Suited for CNC routers, robotic joints, conveyor indexers, 3D printer extruder drives, and other light-to-medium duty DIY transmission builds.

📐 Technical Specifications — Spur Gear

Module (Mod)	1
Number of Teeth	21
Pressure Angle	20°
Material	45# Medium-Carbon Steel
Bore Diameter	6 mm / 6.35 mm / 8 mm (see variant options)
Pitch Diameter	21 mm (0.827 in)
Outside Diameter	Approximately 23 mm (0.906 in)
Face Width	See variant options
Hub Style	Setscrew hub
Finish	Natural steel / lightly oiled
Gear Type	External spur gear
Application	Motor transmission, robotics, CNC, conveyor drives

❓ Frequently Asked Questions

How do I choose the right bore size for my motor shaft?

Measure your motor shaft diameter with a caliper. Select 6 mm for most small stepper and DC motors, 6.35 mm (1/4 in) for motors with imperial shafts common in North American hobby applications, and 8 mm for larger NEMA 23 steppers or brushless motors. The setscrew hub accommodates plain or flat-keyed shafts within each bore size.

Will this gear mesh with my existing Mod 1 rack or pinion?

Yes. Any gear or rack with a Module 1 tooth profile and a matching 20° pressure angle will mesh correctly with this 21-tooth spur gear. Tooth count only affects gear ratio, not compatibility — you can pair it with any Mod 1 mating gear regardless of its tooth count.

Is 45# steel strong enough for my CNC or robotics project?

45# steel (equivalent to AISI 1045) has a tensile strength of approximately 600–700 MPa in its normalized state, making it well-suited for light-to-medium duty transmission applications such as CNC routers, robotic joints, and conveyor indexers. For very high-torque or high-cycle industrial applications, consider a hardened or alloy steel gear instead.

Does this gear resist rust and corrosion?

45# steel is not inherently stainless. The gears are supplied with a light oil coating to prevent surface oxidation during storage and transit. For humid or outdoor environments, apply a thin layer of grease or anti-corrosion spray after installation. For corrosive environments, a stainless steel or plastic gear may be more appropriate.

What gear ratio can I achieve with a 21-tooth spur gear?

Gear ratio is determined by the tooth count of the driver divided by the tooth count of the driven gear. For example, pairing this 21-tooth gear with a 42-tooth mating gear gives a 2:1 reduction ratio. Pairing it with a 7-tooth pinion gives a 1:3 speed increase. You can mix and match any Mod 1 gears to achieve your target ratio.

Can I use this gear with a 3D printer extruder or Z-axis drive?

Yes. Mod 1 spur gears are commonly used in DIY 3D printer extruder gear sets and Z-axis lead screw drives. The 6 mm and 8 mm bore options cover the shaft sizes used by most NEMA 17 and NEMA 23 stepper motors. Verify your printer's existing gear module before ordering to ensure mesh compatibility.

How many gears are included per order?

Each order includes one (1) spur gear in the bore size selected at checkout. If you need a matched gear pair or a complete gear set, simply add the required quantity to your cart or contact us for bulk pricing options.

🛒 Select your bore size above, then add to cart.

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These o rings are a great for my ear tunnels

These o rings are a great for my ear tunnels, always loosing one here and there, I always have a new ones in the drawer. Being silicone, don't have any reactions compared to standard rubber ones I purchased at hardware stores, plus much less expensive. Purchased 16mm I'd to use on 19mm tunnels, and stay on great, might be able to get away with 17mm rings, but really happy with my choice.

Will never order from these folks again

I waited a long time and that’s all I received was the eyebolt with no threaded rod attached to it

Perfect they are really made well and I used them for my car

Perfect they are really made well and I used them for my car. The only thing I had a great for us. It took three weeks to get here. So shipping was slow.

did not include wing nuts

Hi Scott, thank you for your feedback. We're sorry for any inconvenience caused. Please get in touch with us directly, and we'll assist you. Thanks for shopping with HomeDIYer!

Haven't received the order yet! It's been over

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1 Mod 21 Teeth Spur Gears (45# Steel) Transmission Motor Gear Bore 6/6.35/8mm

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DIY Expert Support

Description

1 Mod 21 Teeth Spur Gears — Reliable Power Transmission for DIY Automation

✅ Key Features of These 1 Mod 21 Teeth Spur Gears

📐 Technical Specifications — Spur Gear

❓ Frequently Asked Questions

1 Mod 21 Teeth Spur Gears (45# Steel) Transmission Motor Gear Bore 6/6.35/8mm

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