Ruko hss bi metal hole saws ruko 106025 this 25mm ruko hss bi metal hole saw has varied tooth spacing and is suitable for unalloyed steel up to 700 nmmsup2 strength non ferrous and light metals plastics plasterboard and light building boards fibreboard plywood and wood it is particularly suitable for use with hand drills pillar drills and lathes ruko 106025 hss bi metal hole saw 25mm