The arrowheads AutoCAD LT uses are stored as block definitions. To use your own arrowhead, provide the name of an existing block definition. For information about how to create a block, see Creating Blocks within a Drawing.
Arrowhead sizing relies on the overall dimension scale factor. When you create a dimension, AutoCAD LT inserts your block where the arrowheads would normally go. The object's X and Y scale factors are set to arrowhead size overall scale. The dimension line is trimmed by text gap overall scale units at each end. To trim the dimension line, AutoCAD LT inserts the rightmost block with a zero rotation angle for horizontal dimensioning. The leftmost block is rotated 180 degrees about its insertion point.
If you use paper-space scaling, AutoCAD LT computes the scale factor before applying it to the arrowhead size value.