Stainless Large Bonsai Root Cutters by Roshi Tools 10.6" (269 mm)
Roshi stainless steel bonsai tools are famous for precision cutting, durability and excellent prices.
Root cutters are designed for removing tough old roots. They are especially good for removing roots immediately below the base of the trunk.
Though not usually a beginner's tool, most serious bonsai enthusiasts wouldn't be without one.