Windmills cannot be assembled in a factory and shipped completed to the installation site. They have to be assembled in the field. This is not difficult as it is fairly obvious to any installer as to how to put the windmill together. Factory training is however strongly recommended. It must be emphasized however that a water pumping windmill comprises hundreds of steel components and nuts and bolts. The coming loose of even one of these can lead to the windmills destruction. It is essential therefor that a windmill be revisited a few months after its installation and that every nut and bolt be tightened again. Reputable windmill manufacturers supply bolts with spring washers which have the effect of locking the nut so that it cannot come loose after being tightened however these become ineffective if the initial tightening of the bolt is inadequate.