Concave cutters are specialized tools for pruning bonsai trees. They have curved blades that create a concave wound on the branch, which heals faster and with less scarring than a flat or angled cut. Concave cutters are essential for maintaining the health and aesthetics of bonsai, as they allow you to remove unwanted branches without leaving unsightly stubs or bumps. Concave cutters come in different sizes and shapes, depending on the type and thickness of the branch you want to cut. Some common types are black, stainless steel, and round concave cutters. You can use concave cutters to trim both living and dead branches, as well as to remove bark or knobs from the trunk. Concave cutters are made of durable materials, such as carbon steel or stainless steel, and they require proper care and sharpening to keep their edges sharp and prevent rusting.