15 stands for basic, 16-stands for rutile and 17 for rutile with some SiO2. These are the coating designators. You also have 25 and 26 which are synthetic electrodes with rutile and basic coatings(synthetic means like wire different from weld metal analysis ~ e.g. cs wire and all alloying or part alloying through flux)15,16,17 designate thus not only properties but also usability, in the sense that because of the basic nature of flux, cleanest weld metal expected from 15 type and thus best mechanical properties for welds with these consumables. However the electrodes not so easy to use when compared to 16 or 17 types. 16 by so far is the easiest to use and is most welder friendly and usable in all positions. 17 gives best contour of weld bead as comp[ared to 15 or 16 b'cos of silica but cannot be used in all positions! 25,26 can be used with higher currents without problems of the core wire getting heated up. Having said that the redrying and handling procedures diffrent for all these varieties. Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!