2.3 Non-Threaded Fasteners, Pins, Keys & Anchors

Non-Threaded Pins and Alignment Hardware

Non-threaded pins serve two main functions in mechanical machinery: precise positioning/alignment of mating components and shear-load fastening. Industrial mechanics utilize several distinct pin designs based on load requirements and assembly methods:

Parallel Dowel Pins

Precision ground fasteners manufactured to tight press-fit tolerances (typically +0.0002 to +0.0004 inches over nominal diameter, such as ISO m6 fit). Made from hardened alloy steel (Rockwell C 58–62), dowel pins align split gearbox housings, pump casings, and stamping dies prior to bolt tightening. Bolts provide clamping force, but dowel pins absorb side shear forces and ensure components return to exact alignment whenever disassembled. Unhardened dowels are used where pins must shear intentionally to protect driven equipment during overloads.

Taper Pins

Feature a uniform taper along their length—Standard Imperial taper pins decrease in diameter at a rate of 1/4 inch per foot (1:48 taper), while Metric taper pins use a 1:50 taper. Taper pins fit into holes finished with matching taper pin reamers. Driven home with a mallet, the wedging action provides exceptional concentric alignment and zero-backlash torque transmission for light hubs. Taper pins are easily driven out from the small end during teardowns and re-seat repeatedly without losing position accuracy.

Roll / Spring Pins (Slotted and Coiled)

Hollow tubular pins made of high-carbon spring steel, slotted lengthwise or coiled like a spiral. They are manufactured slightly larger than their target drilled hole. When driven into a standard drilled hole (no reaming required), the pin compresses inward, exerting continuous outward radial spring pressure against the hole wall. Roll pins resist heavy shock and vibration, making them ideal for securing linkages, control levers, and gear shift forks.

Cotter Pins and Clevis Pins

Split wire fasteners installed through holes in clevis pins or castellated nuts. Once inserted, the split ends are bent back around the mating component. Cotter pins act as secondary positive locking devices to prevent nuts or pins from backing out under severe vibration.

Retaining Rings (Circlips)

Retaining rings are resilient metal rings installed into machined internal bore grooves or external shaft grooves to locate, retain, or position parts axially (e.g., holding bearings, gears, and pulleys in place).

• Internal Retaining Rings: Compress inward to fit into a housing bore groove.
• External Retaining Rings: Expand outward over a shaft to seat in a shaft groove.
• E-Rings (Radial Retaining Rings): Open-sided rings pushed radially onto a shaft groove, ideal where end access is blocked.

Installation Best Practices: Retaining rings must be installed using specialized circlip pliers (internal or external). Over-expanding or over-compressing rings causes permanent deformation, destroying their spring tension and seating capability. Retaining rings are manufactured by stamping steel sheet metal, creating one rounded edge (from the punch entry side) and one sharp, burred edge (from the die breakout side). For maximum load capacity, the sharp, flat edge must always face the direction of axial thrust load, ensuring solid contact against the groove wall.

Shaft Keys, Keyways, and Fitting Standards

Shaft keys are removable machine components installed between a shaft keyseat and hub keyway to transmit rotational torque and prevent relative rotation between the two parts:

• Square Keys: Standard specification where key width equals key height ($W = H \approx \frac{D}{4}$ of shaft diameter). Common on shafts up to 6.5 inches (165 mm) in diameter.
• Rectangular Keys: Key width is larger than key height (W > H). Used on shafts over 11/2 inches diameter or where shallow keyways are required to preserve shaft sectional strength.
• Woodruff Keys: Semi-circular keys fitting into a matching semicircular keyseat milled into a shaft by a Woodruff keyway cutter. The key can rock in its rounded seat, making it self-aligning to accommodate tapered shaft ends, pulleys, and flywheels.
• Feather Keys: Fastened into the shaft keyseat using countersunk machine screws. A feather key permits the hub to slide axially along the shaft (e.g., in clutch engagement mechanisms) while continuously transmitting rotational torque.

Fitting Standards: Keyseats are milled into shafts using end mills or side milling cutters, leaving radiused fillets at keyseat corners to minimize stress concentrations. Millwrights hand-fit critical parallel keys using a fine file and machinist's bluing. A properly fitted key must fit snugly on its side flanks (drive faces) to transmit torque without backlash, while maintaining a tiny clearance (typically 0.002 to 0.005 inches) on top to prevent radial binding and hub distortion.

Concrete Anchor Bolts for Machinery Mounting

Anchoring heavy industrial machinery to concrete foundations requires anchor bolts capable of handling static weight, operational thrust, dynamic vibration, and overturning moments:

Mechanical Expansion Anchors

• Wedge Anchors: Heavy-duty steel studs with an expansion clip at the bottom. Driven into a pre-drilled hole in solid concrete. When the nut is torqued, the wedge tail pulls up, forcing the clip outward to bite into the concrete wall. Highly effective in solid concrete, but cannot be used in brick or weak masonry.
• Sleeve Anchors: Feature a full-length tubular sleeve over a threaded rod with a conical expander nut. As the bolt is tightened, the cone draws into the sleeve, expanding it against the hole wall. Ideal for concrete, hollow block, and masonry.

Adhesive / Epoxy Anchors

Chemical anchors utilize two-part synthetic epoxy or polyester resin cartridges injected into a cleaned, drilled hole before inserting a threaded rod or rebar. The resin cures to form a bond stronger than the concrete itself. Epoxy anchors exert zero expansion stress on the surrounding concrete, making them the required choice for anchor placement near foundation edges, close bolt spacing, dynamic/vibratory machinery, or cracked concrete.

Cast-in-Place Anchors

Installed in the foundation formwork prior to pouring concrete. Examples include J-bolts, L-bolts, and sleeve-encased anchor bolts. Sleeve-encased anchors place a pipe sleeve around the top section of the embedded bolt, creating an air gap that allows the millwright to bend the exposed bolt end slightly to align perfectly with machine base mounting holes during equipment setting, after which the sleeve is filled with non-shrink grout.