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https://golovin2017.com/2016/01/08/publications-7-drilling-tool-bogomolov-mining-tool-for-boreholes-with-square-cross-section-boring-tool-of-bogomolov/
Publications #7 – «Drilling tool Bogomolov» - Mining tool for boreholes with square cross-section «Boring tool of Bogomolov»