One of the end supports of each support roller is pivotally mounted for pivoting the support rollers in {HEAD ~ a plane} defined by {TAIL ~ the axes} of the support rollers 
defined by
One of the end supports of each support roller is pivotally mounted for pivoting the support rollers in { HEAD ~ a plane } defined by { TAIL ~ the axes } of the support rollers
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH