Spiral Duct This ducting is made from our R V1923 type material Spring steel wire is welded on to the duct using a special extruded P V C profile with wear protection Standard sizes produced are DIA LENGTH 12 X 25 16 X 25 20 X 25 24 X 25 30 X 25 36 X 25 Standard pitches are 4 and 6 Other combinations can be made to your specification ROCVENT INC MINE TUNNEL VENTILATION 14 wwwrocventcom