130 GREENHOUSES 



od of coupling is that the shafting may be 

 put up in sections and clamped together after 

 being put in place. Square or round, solid 

 shafting is sometimes used, but it has less 

 torsional or twisting strength, weight for 

 weight, than does good wrought-iron or 

 steel pipe. Wrought pipe comes in two 

 weights, standard and extra heavy. It is 

 safe to use the different sizes and strengths 

 as follows: Shafts up to 50 feet in length, 

 i inch standard strength; shafts up to 75 

 feet in length, 40 feet of I inch extra heavy, 

 and 35 feet standard strength; shafts up to 

 125 feet in length, i/4 inch all extra heavy. 



Shaft Hangers. The shafting is held in 

 place by means of hangers. These hangers 



Fig. 70. Shaft hangers 



may be fastened to the rafters, to the sash 

 bars or to the supporting posts. In iron frame 

 houses it is customary to hang overhead 

 shafting from the rafters and the shafting 

 for the side ventilators from the side posts, 

 using a hanger for each rafter or post. 



