TheShearPinisoneoftheservicepartsofthebreathingsystem.Ashearpinisnormallycutfromtheshearstock.Usuallytheshapeofshearstockisarodform.Itisthesolidpinwhichhastheroundheadthatavoidthepinm ovementintotheoppositeendofthedrilleddownhole.Theoppositeendhasadrilledholeof2mmdiameter,whichisusedtoinsertcotterhairpin.Theshearpinisasafetytooldesignedtobrakeandstopthemachineincase ofoverload,whichismachinedatacriticalpoint.Itisusedtopreventdamagefromotherpartsandalsoasaconditionaloperatorthatwillnotallowthedevicetooperateuntilthecorrectforceisapplied.Itprovidesadistinctthresholdforcefortherequiredoperation.