Many tasks must be performed with two hands (e.g., lifting a large two-handled platter of food or a bulky package). Such tasks do not require hand differentiation; each hand (and arm) does essentially the same thing. For assessment of hand differences on bimanual tasks, the hands must be used in different but complementary ways. Examples include opening a jar, where one hand grips and turns the lid while the other hand stabilises the jar or even turns it in the reverse direction, or painting, where one hand wields the brush while the other holds the palette. There is a fine line between certain unimanual and bimanual tasks. For example, one hand may be sufficient for hammering a nail into wood, but the task initially is bimanual since the other hand holds the nail still until it is securely in place. Likewise, bread can be cut with one hand but, normally, the other hand holds the bread stable.
See Ambidexterity, Finger-tapping task, Hand preference, Hand proficiency, Handedness (bi-manual vs uni-manual), Handedness (general), Lateral bias, Laterality. Unimanual task