Jar Lids: Effect of Diameter, Gripping Materials and Knurling

Abstract
In Exp. 1, 10 female subjects each twisted six jar lids vs a torque meter with a bare hand, rubber gripper and a cotton cloth. The torques of 3.17 Nm for the 48 mm dia, 5.02 for the 67 mm dia, and 6.04 for the 86 mm dia lids differed significantly. Torques of 4.04 for the cotton cloth in the hand, 4.85 for the bare hand and 5.36 for the rubber gripper also varied significantly. The 4.66 Nm for non-knurled was not significantly different from the 4.84 for knurled. Exp. 2 replicated Exp. 1 with 5 of the 6 lids for 29 visitors to a University Open House. The results were compatible with Experiment 1. Torque exertable on a lid can be predicted well from grip strength, lid radius and the gripping material (rubber, bare hand or cloth).

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