a guide member slidably mounted on {TAIL ~ said head} in {HEAD ~ a direction} parallel to the axis of said measuring element 
a guide member slidably mounted on { TAIL ~ said head } in { HEAD ~ a direction } parallel to the axis of said measuring element
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH