Lots of manual actions and hundreds of material objects can be used to form a concept of a line. Intentional grasp is associated with attention to more universal objects, which makes finding objects for them much easier than the highly personal objects required within ACL 2.
Common manual actions include washing, brushing, wiping, colouring, painting, folding, dropping, throwing, tearing, stacking and spreading.
The simplest shape for surfaces to place objects on seems to be a rectangle, which has corresponding horizontal and vertical lines.