Technical Foundation
What Is a Spring Pin?
A spring pin (roll pin) is a hollow, split or coiled cylindrical pin manufactured slightly larger in diameter than its nominal hole size, so it compresses as it's driven in and exerts continuous outward spring force against the hole wall, creating a secure friction fit without requiring the precisely reamed hole a solid dowel pin needs. This tolerance-forgiving installation — a drilled (not reamed) hole is sufficient — is the main reason spring pins are far more common than solid pins in general assembly work.
Slotted spring pins are rolled from flat stock into a cylinder with a single lengthwise slot/gap, giving moderate spring force and shear strength at low cost. Coiled spring pins are wound from several turns of material into a helical coil, giving more uniform, higher spring force distributed around the full circumference, better shear strength and better performance under cyclic or shock loading — the standard upgrade where a slotted pin has shown signs of loosening or shear fatigue in service.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Construction | Slotted (single-slot rolled) vs. coiled (multi-wrap) | Coiled pins give more uniform spring force and better shear/fatigue performance |
| Hole Tolerance | Standard drilled hole (not reamed) | Spring pins accommodate normal drilling tolerance — no reaming needed unlike solid dowel pins |
| Diameter | Sized per ASME B18.8.2, slightly oversized vs. hole | Oversizing generates the spring force that retains the pin in the hole |
| Material | Carbon steel, stainless steel, alloy steel | Determines shear strength and corrosion resistance for the application |
| Chamfer | Chamfered ends standard | Eases starting the pin into the hole and reduces shaving of the hole wall during installation |
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Applications
Where Spring Pins Get Used
Spring pins are specified anywhere a shaft, lever or pivot needs secure retention using a standard drilled hole, without the cost of reaming required for a solid dowel pin.
Hinge & Linkage Pin Assemblies
Coiled spring pins retaining hinge pins and linkage joints subject to repeated articulation and light shock.
Machine Guard & Access Panel Retention
Slotted spring pins securing removable guards and panels that need occasional disassembly for maintenance access.
Automotive & Small Engine Assembly
Spring pins locating and retaining small components like shift forks, levers and detents in gearboxes and linkages.
Electrical Enclosure & Panel Hardware
Spring pins retaining hinge and latch hardware on electrical enclosures and control panel doors.
General Machine Assembly
Spring pins used broadly wherever a shaft, lever or component needs secure retention without a reamed hole or threaded fastener.
Firearms & Precision Mechanisms
Small-diameter coiled spring pins retaining pins and components in mechanisms requiring reliable, repeatable retention force.
FAQ
Spring Pins Questions, Answered
Do I need to ream the hole for a spring pin like I would for a dowel pin?
No — this is the main advantage of spring pins. Because the pin is manufactured slightly oversized and compresses as it's installed, a standard drilled hole (within normal tolerance) is sufficient to develop a secure friction fit. A solid dowel pin, by contrast, needs a precisely reamed hole to achieve the same reliable fit.
Should I use a slotted or coiled spring pin?
Coiled spring pins, wound from multiple wraps of material, distribute spring force more evenly around the full circumference and offer better shear strength and fatigue resistance under cyclic or shock loading — the better choice for hinges, linkages and any application with repeated movement. Slotted pins are simpler, lower-cost, and adequate for lighter-duty, more static retention applications.
Can spring pins be reused after removal?
Generally not recommended — once a spring pin has been compressed and released, its spring force is somewhat reduced compared to a fresh pin, and repeated reuse further degrades the fit. For anything beyond a one-time diagnostic removal and reinstall, replacing with a new pin restores full retention force.
How do I determine the correct spring pin diameter for my hole?
Spring pins are sized per ASME B18.8.2 to be nominally larger than the stated hole size by a controlled amount that produces the intended interference/spring fit — order by the nominal pin size matching your hole's nominal drilled diameter, not by measuring the pin itself, since the pin is intentionally oversized before compression.
What's the benefit of a chamfered end on a spring pin?
The chamfer eases the pin into the hole opening and reduces the risk of the pin's edge shaving material off the hole wall during installation, which could otherwise reduce the fit's retention force or leave metal shavings in the assembly. Nearly all standard spring pins include a chamfer on at least one end.
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