It is a tool used to grind the objects falling into the well and shear the fish top.

The mill shoe is a rotary cutting tool designed for downhole milling operations, including the removal of debris, section milling of casing, window cutting for sidetracking, and dressing of fish tops prior to fishing. Manufactured in compliance with API Spec 7K, this tool features a cutting face embedded with tungsten carbide inserts or crushed tungsten carbide material that grinds away metal and formation material when rotated under weight. Available in various configurations including flat-bottom, concave, tapered, and pilot types, the mill shoe is engineered to match specific milling applications while maintaining optimal cutting efficiency and fluid circulation.