Abstract: A polishing-grindstone mount base assembly has a mount cassette formed of hard rubber. The mount cassette includes a wedge-shaped rib, having a dove-tail-shape in cross-section for engaging the arm of a conveyor-type plane polisher. The mount cassette is fixed to the mount base with bolts of a synthetic resin which will break on excessive impact, allowing the base for separate from the mount to prevent damage to the base. The base has an abrasive layer on the bottom surface, and protective layers of synthetic resin on each side of the abrasive layer to prevent breaking of the abrasive layer.