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Flex Head Ratchet Wrench

The manufacturer of a flexible head ratchet wrench required an alternative to a Grooved Pin.



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.

A Coiled Spring Pin’s pre-installed diameter is larger than the intended hole. During installation, the Coiled Spring Pin is compressed within the hole. The Coiled Spring Pin then functions as a spring and recovers within the hole. This allows the pin to conform to the hole wall thus ensuring maximum contact over the full length of engagement. The dynamic nature of the Coiled Spring Pin also allows it to provide good retention over a much greater total hole tolerance than the Grooved Pin.



SPIROL Engineering recommended a heavy duty Coiled Spring Pin for use in this application. This pin corrected the retention problem by maximizing interference within the limited available length of engagement. This pin provided adequate strength while maintaining enough flexibility to absorb shock and excessive loading without damaging the hole. Hole integrity must be maintained to ensure long retention as well as proper ‘fit & function’. The recommended product was from SPIROL’s standard offering thus providing a low cost solution that could be provided quickly for evaluation and testing.

Complimentary Applications Engineering Support: SPIROL Engineers will review your application needs and work with your design team to recommend the best solution.