**Simple and direct answer: Not exactly the same, but they are often used interchangeably in practice. Strictly speaking, "Swivel Radius" is the physical result of "Offset."**

To help you completely distinguish between these two concepts, you can understand them from the following three dimensions:

1. Different Definitions (Physical Essence)

- **Offset (also known as Kingpin Offset or Swivel Lead):**

    - Refers to the **horizontal distance from the vertical line of the central rivet/kingpin (the center of the caster's rotation) to the center of the wheel (the wheel axle)** .

    - This is a **design dimension** – a fixed parameter determined by the caster manufacturer when designing the frame (rig). It determines whether the wheel will self-center when swiveling and how easy it is to steer.

- **Swivel Radius:**

    - Refers to the **radius of the circle traced by the outermost edge of the wheel as the caster (frame) rotates 360 degrees around its vertical axis** .

    - This is a **movement path** – the actual amount of space the caster occupies during a turn. It is usually equal to the "Offset" plus the "Radius of the Wheel" or the dimension of a specific protruding part of the wheel.

2. Understanding with a Diagram

Imagine looking down at the caster from above:

- **Offset** = The horizontal distance from the center point of the rivet/kingpin to the center point of the wheel.

- **Swivel Radius** = The distance from the center point of the rivet/kingpin to the **outermost edge of the wheel**.

*Note: It is precisely because of the "Offset" that the wheel can swivel around the rotation axis, thus drawing that circle. Therefore, the Swivel Radius is usually greater than the Offset.*

3. Numerical Relationship

Generally speaking: **Swivel Radius = Offset + Wheel Radius (or the horizontal distance to a specific point on the wheel)** .

- **Key Point:** If a caster has an Offset of 40mm and a wheel radius of 50mm, its Swivel Radius is approximately 90mm. While the Offset determines steering flexibility, the actual space required for your cart to turn is determined by that **90mm (Swivel Radius)** , not the 40mm (Offset).

Summary

- If you are **designing a caster structure** and need strict differentiation: **Offset is the cause, Swivel Radius is the result.**

- If you are **selecting a caster** and are concerned about "whether the wheel will hit the frame (interference)" or "how much space is needed to turn," the dimensional parameter usually provided by the merchant is the **Swivel Radius**, although many people habitually call it "Offset."

**Conclusion: They are not the same physical quantity, but they are highly related.**

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I hope this translation is helpful. Let me know if you need any other adjustments.