{TAIL ~ A preferred embodiment} of {HEAD ~ machine} is self contained and portable, configured for easy and quick changing of the friction surface, and provides for rotating the test sample about an axis normal to the sliding surface and the direction of movement of the sample relative to the friction surface 
{ TAIL ~ A preferred embodiment } of { HEAD ~ machine } is self contained and portable , configured for easy and quick changing of the friction surface , and provides for rotating the test sample about an axis normal to the sliding surface and the direction of movement of the sample relative to the friction surface
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH