Sentence:  The <WSD>bolter</WSD> was basically a sheet or roll of wire mesh or cloth (most often canvas or linen, but sometimes silk or another fabric). The flour produced by the mill was fed through or over the device, which was shaken by a mechanism (several were possible) taking power from the drive train leading from the water wheel to the millstones. 
Meaning of the word marked with <WSD> tags:  A machine or mechanism that automatically sifts milled flour.