from the manual:
....
ent_bonename(ENTITY*,STRING*,var num)
Gets the name or handle of a bone that controls the vertex with the given number.

Parameters:
ENTITY* entity pointer
STRING* string to be set to the bone name, A7.08 or NULL for returning the bone handle
num number of a vertex attached to the bone.

Returns:
Bone handle if the bone was found, otherwise 0.
....

i want to use them because handles work faster than bone names