Controlling dimension arrows  

You can control the appearance and size of arrowheads or tick marks placed at the ends of dimension lines. Any changes you make affect the current dimension style. The arrowheads you choose display in the image tile on the right side of the Dimension Styles dialog box.    

You can choose from a number of arrowhead types. You can specify different arrowheads for each end of a dimension line and for leader lines. The Starting arrow corresponds to the first extension line; the Ending arrow corresponds to the second extension line. Blocks defined in the drawing also display in the three Arrowhead lists as user-defined arrows. You can use these blocks to create and assign your own arrowheads.

The Arrow Size value determines the size of the arrowhead, measured in drawing units. You can also use tick marks instead of arrowheads.    

To choose an arrowhead

   1   Do one of the following to choose Dimension Styles Manager ():

    On the ribbon, choose Annotate > Dimension Styles Manager (in Dimensions).

    On the menu, choose Dimensions > Dimension Styles Manager or choose Format > Dimension Styles Manager.

    On the Dimensioning or Styles toolbar, click the Dimension Styles Manager tool.

    Type setdim and then press Enter.    

   2   Click the Symbols and Arrows tab.

   3   In the Starting Arrowhead or Ending Arrowhead list, click to select the starting or ending arrowhead, respectively. If necessary, mark Allow Separate Arrowheads if you want to use different starting and ending arrowheads.

   4   In the Leader Arrowhead list, click to select a leader arrowhead for leader lines.

    5    Click OK.

Use the system variable.  
The DIMLDRBLK system variable also specifies leader arrow types.