High Carbon Steel Large Spherical Knob Cutter by Koyo 11.5"
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 serious bonsai enthusiasts wouldn't be without one.
11.5" Made in Japan by Koyo, a quality tool maker