Human Factors and Behavioral Science: Effects of Shape and Size of Knobs on Maximal Hand-Turning Forces Applied by Females

Effects of Shape and Size of Knobs on Maximal Hand-Turning Forces Applied by Females By G. A. KOHL* (Manuscript received December 23, 1981) Outside plant craftspeople use knobs to apply turning forces on clamp mechanisms that hold field equipment temporarily in place. A study was performed to develop a set of data that provide guidance for determining knob size and shape characteristics most appropriate for various outside plant working conditions. Forty female participants applied maximal isometric turning force to each member of a set of twenty experimental knobs that systematically varied in shape and size. In half the trials the participants applied force with greased hands and in the other half used nonslip compound. In addition, two arm-wrist positions were observed. In general, triangular knobs allow more hand torque to be generated and require significantly less material than square, pentagonal, hexagonal, or circular knobs of comparable size. However, this effect depends upon the arm-wrist position and grip conditions. A 3.5-inch turning diameter is desirable when both cost and performance are considered. I. INTRODUCTION Outside plant craftspeople in the Bell System use knobs to apply turning forces on screw-operated clamp mechanisms used to hold heavy field equipment temporarily in place. Female craft who use these * Bell Laboratories. °Copyright 1983, American Telephone & Telegraph Company. Copying in printed form for private use is permitted without payment of royalty provided that each reproduction is done without alteration and that the Journal reference and copyright notice are included on the first page.