About this 3D model

For use with [Prusa i3 Rework](http://reprap.org/wiki/Prusa_i3_Rework_Introduction) version ONLY. 40 mm fan shroud for J-Head Hotend Update 12/23/13 - I found a problem when I tried it on a new extruder body for a second printer. So I redesigned it to fit better and re-uploaded.