Kaneshin No. 4S Concave Cutter is smaller in size than the No. 4 at a length of 6.5″ long. The cutting edge on the No. 4S is rounded making these act as a concave cutter and a knob cutter in one tool. These work well on smaller sizes of bonsai. Concave cutters are designed to create a clean concave cut. You can use them to cut branches and other things or use them to make the edges of wounds cleaner.