Flex Head Ratchet Wrench
The pin functioned as a pivot/axle on which the head would rotate. The Grooved Pin did not provide adequate retention and ‘walked’ from the hole during cycle testing. The wrench carried a lifetime warranty and the customer wanted to eliminate this failure mode.
The wrench provided pin retention in the middle hinge component, or head. A free fit was required in the outer hinge elements or handle. The customer required a large hole tolerance in the head to allow tuning for desired ‘fit & function’. Grooved Pins are static rather than dynamic. The total hole tolerance for most Grooved Pins is approximately .002”. If the hole is too small the pin cannot be installed – too large and it will fall out of the hole. In this case the customer’s required hole was slightly larger than recommended. The grooves in many Grooved Pins are manufactured via a process that forms a crescent shaped retention feature. If installed in an oversized hole, this form will only make contact at a single point. This allows movement of the pin within the hole. Under the large loads applied with this wrench, the pin could ‘rock’ within the hole until it eventually walked out.
Installation of a Grooved Pin requires the displacement of material from pin or hole. The result is a press fit with limited contact between the pins groove ‘peaks’ and the host.