US1274928A US23215418A US1274928A US 1274928 A US1274928 A US 1274928A US 23215418 A US23215418 A US 23215418A US 1274928 A US1274928 A US 1274928A Authority US United States Prior art keywords block plates emery plate strips Prior art date 1918-05-02 Legal status (The legal status is an assumption and is not a legal conclusion