Creating and Modifying Custom Arrowheads
To use your own arrowhead symbol
- From the Dimension menu, choose Style.
- In the Dimension Styles dialog box, choose Geometry.
- In the Geometry dialog box under Arrowheads, select User Arrow from the 1st arrowhead list.
- In the User Arrow dialog box, enter the name of your block. Then choose OK.
- To choose a different custom arrowhead for the second arrowhead, repeat steps 3 and 4, choosing User Arrow from the 2nd arrowhead list.
- Choose OK to exit each dialog box.
Dimension toolbar: 
Command line equivalent: DDIM