SPRING 2025

48THE DISTRIBUTOR’S

48THE DISTRIBUTOR’S LINKSPIROL INTERNATIONAL CORP.30 Rock Avenue, Danielson, CT 06239TEL 1-860-774-8571 FAX 1-860-774-2048 EMAIL info@spirol.com WEB www.spirol.comTHE BENEFITS OF LIGHT DUTY COILED SPRING PINS INSOFT AND BRITTLE MATERIALS by Adolf Valasek, Applications EngineerGeneral Benefits of Spring PinsSpring Pins are mechanical fasteners used for avariety of functions including: hinging, aligning, and joiningtwo or more parts together. Their method of retentionis by radial tension that results from their interferencewith the host component. The key difference to otherfastening methods that rely on interference is that SpringPins are designed to be the compliant, flexible elementof the joint. Spring Pins exert a constant radial tensionagainst the hole wall and can protect the host componentfrom incurring deformation or other permanent damageto the hole. Thanks to its flexible diameter, Spring Pinsalso allow for a much wider hole tolerance, lowering themanufactured cost of the host component.“Spring Pin” is a general term, however. There areother types of fasteners that satisfy the above definition,of which two are the most prevalent – Slotted SpringPins and Coiled Spring Pins. Slotted Spring Pins are bestknown by their C-shape cross section, while Coiled SpringPins have a 2 ¼ coil cross section and present the moreflexible option as they are made of multiple wraps ofthinner material and do not have a slot that would limit itsflexibility when it closes.The Three Duties and DifferencesBetween ThemThe Coiled Pin is available in three duties – Light,Standard and Heavy – so designers have the option tochoose the optimum balance of strength, flexibility anddiameter of the pin for their specific application. All threeduties have the same 2 ¼ coil formation with the corephysical difference betweenthem being the thicknessof the raw material - andsubsequently their flexibilityand strength.Typically, the optimum“Duty” is driven by the hostmaterial of the applicationand its strength/hardness aswell as the actual functionalrequirements of the pin withinthe assembly. Light Duty isrecommended for plastics, soft metal castings (such aszinc and aluminum die castings) and brittle materials suchas ceramics. Standard Duty is recommended for mildsteels (such as unheat treated steels and cast iron) andnon-ferrous metals (such as bronze and aluminum), whileHeavy Duty is reserved for hardened steels or severeshock and vibration environments. Host material type,however, only limits the use of the heavier duties, withthe goal being to design in a pin that is strong enough towithstand the applied load, yet flexible enough to isolateand protect the soft or fragile hole material from theforces.LEFT: COILED SPRING PINS,RIGHT: SLOTTED PINCOILED SPRING PINS ARE AVAILABLE IN HEAVY, STANDARD, ANDLIGHT DUTYTECHNICAL ARTICLE CONTINUED ON PAGE 112