Bonsai Knob Cutter by Roshi Tools 6.8" (179 mm)
Knob Cutters are designed for removing unsightly knobs from trunks and branches without leaving protruding callous when the cut heals. They can also be used to further hollow out the cut after a concave branch cutter is used. Be careful not to overdue it with your knob cutter, they can take bigger bites than expected.
Though not usually a beginner's tool, most bonsai artists wouldn't be without one.
Roshi high carbon steel bonsai tools are known for precision cutting, durability and excellent prices.