Complete Guide to Parallel Key Installation and Size Selection｜The Key Component for Secure Shaft-to-Component Connection
- 翰君 陳
- Aug 13
- 2 min read
Updated: Aug 26
In mechanical transmission and assembly, the parallel key is a small yet crucial component that determines whether parts operate securely. Installed between the shaft and hub (such as gears, pulleys, and couplings), it transmits torque and prevents relative sliding.
If the size is chosen incorrectly or installed improperly, it can lead to loosened parts, reduced mechanical precision, or even shaft damage.
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How to Select Parallel Key Size
Selection is mainly based on shaft diameter and application requirements.
1. Shaft Diameter Correspondence (Common JIS B 1301 Examples)
Shaft Ø 6–8 mm → Key size 2 × 2 mm
Shaft Ø 10–12 mm → Key size 4 × 4 mm
Shaft Ø 14–18 mm → Key size 5 × 5 mm
Shaft Ø 20–24 mm → Key size 6 × 6 mm
Shaft Ø 28–38 mm → Key size 8 × 7 mm
ⓘ Length tip: Slightly shorter than hub slot length (about 0.5 mm) to avoid protrusion or interference with other parts.
2. Material Selection
Carbon Steel S45C – General use, cost-effective
Stainless Steel SUS304 / 316 – Excellent corrosion resistance; suitable for food, medical, and outdoor applications
Heat-treated Keys – For high-load, high-wear environments
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Pre-Purchase Checklist
Before purchasing, check these 4 points:
Shaft diameter and keyway dimensions – Must comply with JIS B 1301
Material – Choose carbon steel or stainless steel based on environment
Length – Matches hub width without protrusion
Surface treatment – Consider zinc plating, passivation, or other protection
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Parallel Key Installation Method
The parallel key’s job is to lock the shaft and hub tightly together. Think of it like “fitting a bite guard onto the shaft”:
Inspect Keyway – Shaft and hub keyways must be clean, burr-free, and match the key size.
Place the Key – Insert into shaft keyway with the flat side parallel to the shaft’s outer surface. If chamfered or round-ended, point chamfer toward insertion direction for easier fitting.
Push in the Hub – Align hub keyway and slide it onto the shaft slowly. Use a rubber mallet if necessary to avoid scratches.
Check Fit – Key should be fully seated without lifting; hub should rotate smoothly.
Tips:
Apply light lubricant to prevent rust and seizing
For heavy-duty use, choose heat-treated keys for better wear resistance
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Common Applications
Mechanical transmission systems (gears, pulleys, sprockets)
Automation equipment and conveyor mechanisms
High-precision positioning devices
Pumps, compressors, coupling fixation
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Why Choose Sheng Fong Precision?
Selecting a parallel key isn’t just about buying a part—it affects the stability and lifespan of your entire system.
Sheng Fong Precision offers more than just products that meet JIS B 1301 standards:
Full range of sizes – From small shafts to large industrial equipment
Multiple materials – S45C carbon steel, SUS304 / SUS316 stainless steel, with heat-treated options available
Quality control – Strict inspection of dimensions and surface treatments for secure installation
Fast delivery – In-stock items, small-batch, and urgent orders supported
Expert advice – Guidance on installation and size selection to reduce assembly risk
Contact us now for parallel key selection advice via LINE (ID: @s9000)
For the complete list of specifications and sizes, please refer to: https://lihi3.me/l2o90
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