The maximum torque a seated operator can apply in turning a knob with the bare thumb and fingertips of his right hand was determined. Effort was made to develop a procedure by which a given knob or set of knobs may be evaluated with respect to maximum torque exertable. A set of 60 knobs, each 1/2 inch thick, was used. The knobs had 20 diameters from 1/8 to 5 inches. For each diameter there were three different rim surfaces: mooth, rectangular-knurl, and diamond-knurl. Each of 45 subjects was tested with every diameter-surface combination. In addition, 15 of the subjects repeated the experiment. The maximum torque exertable increased with knob diameter. For all knob sizes, rectangular- and diamond-knurled knobs permitted greater torques than did smooth kno s. Very little difference in maximum torque exertable was observed between the rectangular and diamond-knurled surfaces.