The metal tips at the end(s) of a knife’s handles.  There are dozens of specialized names for the different styles of bolsters. On a jack knife the bolster opposite the blade-pivot end is called the “top”, or “head”, or “cap” bolster.  The bolster at the blade-pivot end is the “bottom” bolster. A jack knife with no cap bolsters is called a “barehead jack.”   A knife with no bolsters is called a “shadow.”