Bowl Head Adaptor
Bolex Product Code PIBOL (Head 3)
Bolex introduced a bowl head adapter which could provide perfect leveling of the tripod when used on uneven ground.
You can spot when a second type of tripod has this feature by looking under the head and parallel to the legs should be a round handle protruding 5 inches from the head.
When unscrewed this loosens the bowl head which can be moved in all directions so as to level the tripod when on uneven ground using the built in spirit level.