slat the rolling steel door is indicated generally by reference character 32 in fig3 door 32 is of course made up of a plurality of slats such as interlocking steel slat 10 the door is raised by being rolled up on a cylinder 37 to which the door is bolted in a conventional manner cylinder 37 is turned by pulling on a chain 34 which turns a sprocket 35 which is attached to the same shaft as a small gear 36 39 which turns gear 44 which in turn is attached to the central shaft 38 shown in further detail in fig6 in order to facilitate a raising and lowering of larger doors a counterbalance spring 61 is typically used for smaller doors such spring is not necessary but for most commercial doors such spring is appropriate to counter balance the weight of the door as shown in fig6 and 7 door 32 is held to an outer cylinder 37 by clamps 69 outer cylinder 37 is supported by shafts 38 and 39 which shafts are in turn held by end plates 40 and 41 through bearings 42 and 43 end plates 40 and 41 are bolted to the structural wall in a conventional manner shaft 38 supports gear 44 which in turn is moved by gear 36 as described above in order to open and close the door gear 44 is affixed to shaft 38 which in turn is affixed to outer cylinder 37 through a welded plate 45 and a free plate 46 which is secured to the inner end 47 of shaft 38 by a bolt 48 outer cylinder 37.