But if it can be used with thick walls. It is not necessary to use the space, but at least.If the task can use the thick tube is 0.014 ", it is possible to manufacture the coil fins as FPI away stage 12.
You can use pipes with wall thickness up. It is not necessary to be a gap at least if this work can be used as pipe thickness 0.014 ", it is possible to produce a coil spacing is 12 FPI.