path, diameter, method
徑 centers on a direct route or measurement across something: a path or shortcut, the diameter of a circle, or a method as a way to proceed.
徑 combines 彳 (step, go) with 巠, which likely contributes the sound and the idea of a straight or direct line. The modern simplified form is 径.
The left side 彳 suggests movement, and the right side 巠 looks like a straight line with a measuring mark. Imagine walking a direct path and measuring its width: that's a path, a diameter, or a method.
For ケイ, picture a straight path marked with a big letter K: K -> ケイ, and you follow the K-shaped path as your method.