15.64.4  ARROW 

SET ARROW [SIZE=n] [FLARE|FLAIR=n] [PERMANENT]
     1.  SIZE=n  -  length  of arrow head in tenths of an inch.  The units
         may be modified by SET UNITS CHARACTER.
         (Default:2)
     2.  FLARE=n  -  is  ratio of the base to the height of the arrow head
         (fatness).
         (Default:0.2)
     3.  PERMANENT - Makes the current setting the new default.

If no options are specified all parameters are set to the default.