The gray wedge shown in the image, placed under the sharpening stone, has a very specific and helpful function: it maintains a consistent sharpening angle, in this case 15°, as marked on the wedge itself.

Main Function:

It helps keep the knife blade at a fixed angle relative to the sharpening stone.

Ensures consistent sharpening, which is key to achieving a sharp and even edge.

Makes the process easier, especially for those without much experience sharpening freehand.

How it’s used:

The wedge is placed under one end of the sharpening stone to tilt it.

When the knife is laid flat on the tilted stone, the edge aligns with the preset angle (15° or 25°).

This allows the user to focus on moving the blade along the stone, without worrying about keeping the correct angle manually.

15° vs 25° — What's the difference?

15° angle:

Creates a sharper, more precise edge.

Ideal for Japanese knives, filleting knives, and chef’s knives that are used for delicate slicing and precision work.

These knives cut cleaner but may dull more quickly if used on harder materials or bones.

25° angle:

Creates a more robust, durable edge.

Suitable for Western-style knives, hunting knives, utility knives, and outdoor or survival knives.

These blades hold up better to rough use, hard materials, or tasks like chopping or cutting through bone.