A layer of paint, a spring washer or a soft part, such as an O-ring, compresses under the clamp force. This relaxation, or creep, is most obvious and dramatic right after force has been applied. In most joints, creep appears within the first 10 to 50 milliseconds. However, some joints can take a long time to settle. Residual torque measured 1 hour after assembly can differ significantly from residual torque measured a day later.
Residual torque can also be higher than dynamic torque.
To test a joint after it's been fastened, the operator must overcome friction to start the fastener rotating again in the tightening direction. An accurate reading depends on the operator's ability to stop the moment he sees movement. This occurs when torque applied to one fastener affects another fastener in the same assembly. Changing the fastener installation sequence often solves the problem. Because of these problems, fastening experts advise assemblers to avoid putting much stock in differences between dynamic and residual torque measurements.