flour numbering

hi,am new to the art of bread making ,am a cheat and have bought a bread maker ,only trouble all recipies call for flour in numbers i.e. 405, 550, 812, 997. 1050, 1150. 1205,  any body advise me as to what these mean in "plain language"  vis; plain white,strong white etc ,etc, all help and replies very much appreciated   ,,, cowboy,,, newbie baker from kettering uk