The dual sternum strap adjuster, also known as the three-stop buckle, is a commonly used material on backpacks. The raw material is generally nylon or ACE. It is one of the standard spare parts on the backpack, and the general bag will have one or two such buckles. Generally used to adjust the webbing.

The one-way sun buckle is a strap on the backpack. It is generally used to fix the chest strap in front of the chest strap. The dual sternum strap adjuster is fastened on the vertical webbing of the strap, and the one-way buckle is connected to the horizontal webbing on the chest, which can be moved up and down. This design allows the backpack to close the straps to the chest when the backpack is carried, without hindering the movement of the arms. But this kind of buckle is one-way, so if the chest strap is pulled too tightly, the vertical webbing of the strap will be deformed, so it is generally not used for large-capacity backpacks.
The two-way adjustable sun-shaped buckle is usually used on the strap to connect the chest strap. The horizontal strap with this kind of buckle is generally a webbing sleeve, which covers the strap, not just the vertical webbing of the strap. So it doesn't matter how tight it is. Generally used in large-capacity bags.