Parallel Keys with Round Ends vs. Flat Keys — Why They’re Easier to Install and More Durable
- 翰君 陳
- Oct 9
- 2 min read
Although it may look insignificant, the flat key plays a crucial role in preventing slippage and ensuring stable torque transmission between rotating components.
But did you know there’s an upgraded version that’s even easier to install and more durable — the Parallel Key with Round Ends?While it looks almost identical, its rounded ends greatly improve installation efficiency and service life.
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What is a Parallel Key with Round Ends?
A Parallel Key with Round Ends is a type of flat key whose two ends are machined with an R-shaped curve, manufactured according to the JIS B 1301 standard.
In simple terms, it locks components onto a shaft so they rotate together without slipping.Compared to the traditional square-end flat key, the rounded design slides smoothly into the keyway, making installation and removal easier while reducing wear on the key slot edges.
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Key Differences Between Flat and Round-End Keys
Comparison | Flat Key | Parallel Key with Round Ends |
Shape | Square ends | Rounded ends for smoother insertion |
Installation | Needs hammering and alignment | Slides in easily, even by hand |
Removal | Often requires tools to pry out | Round ends make removal easier |
Impact on Keyway | Sharp corners may damage edges | Rounded ends distribute pressure evenly |
Durability | May seize or deform over time | Longer life with balanced stress |
Typical Use | Motors, gears, pulleys | Machine tools, automation systems |
Overall, round-end keys cost only 5–10% more than standard flat keys, due to the extra machining (R-end) and tighter precision requirements — a small price for much higher convenience and longevity.
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Features, Materials, and Applications
Main Feature | Recommended Material / Treatment | Typical Applications |
Stable torque transmission, anti-slip | S45C carbon steel (heat-treated) | Motor & gear positioning |
Easy installation / removal, no damage to shaft | SUS304 stainless steel | Couplings & drive shafts |
Long-term stability, anti-looseness | S45C (heat-treated) / SUS316 | Pumps, compressors, linkages |
High-precision fit, repeat assembly | SUS316 stainless steel (chemical-resistant) | Machine tools, automation systems |
Corrosion & rust protection | SUS304 / SUS316 (passivated) | Outdoor or humid environments |
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How to Choose the Right Size
When choosing a parallel key with round ends, the goal is a perfect fit — not too tight, not too loose.
Example: 10 × 10 × 15 S45C
Width (10 mm) → Matches keyway width
Height (10 mm) → Matches keyway depth
Length (15 mm) → Matches the hub thickness
✔ Match the key size to the shaft diameter.
✔ Confirm the keyway depth so the key neither protrudes nor under-engages.
In short:
Choose a key that slides smoothly into the slot without play.If unsure, just tell us your shaft diameter — Sheng Fong Precision will recommend the optimal size.
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Why Choose Sheng Fong Precision?
Complete materials → S45C, SUS304, SUS316
Standard-compliant sizes → JIS B 1301 / DIN 6885
Reliable quality → Every batch checked for size & tolerance accuracy
Flexible production → Supports small-lot orders & custom lengths / surface finishes
Expert support → We’ll help you choose the right key for your application
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📩 Contact us via LINE (ID @ s9000) for quick key selection advice.
🛒 View the full specifications: https://lihi3.me/wD5X9
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