Thanks I did have 342 343 344 this in a mega entmake. The tblobjname is not working and the help refers to the handle.
(cons 342 (cdr (assoc 330 (entget (tblobjname "block" "_Oblique"))))); DIMBLK
OK found the answer (tblobjname "block" "_Oblique") may work it seems that the block say "_Oblique" does not exist till such time as you modify the arrow head in a existing style or the simplest way around seems to be use (setvar 'DIMBLK ,1 & 2 to what you want 1st. Then entmake using 342 343 344.