A retention fastener solves attachment applications where the design intent is simply to keep two separate materials joined or positioned in a specific arrangement. Retention fasteners can be broken down into two main categories: pin-style and clip-style. Both pins and clips function on the basis of providing a shear barrier to materials sliding out of place. A door hinge’s pin provides us a great illustration of what this means: for the door to fall off of its hinges, the pins within the hinges would have to have so much perpendicular force applied that they’d shear clean apart, as if they were cut with a saw where the hinges’ fingers meet. In other words, we’re using pin and clip fasteners to keep materials joined or positioned by resisting shear forces driving them apart. With that in mind, let’s dive in!
Pin-Style Retention Fasteners
To visualize a pin-style fastener, think of a writing pen to start: long, cylindrical, and fits in your hand. Pin fasteners are very similar – they too are cylindrical, usually longer than they are round, smooth, unthreaded, and most often small enough to handle with one hand. Pins come in a variety of styles, but share one common feature: they’re intended to be inserted into penetrations through materials, binding the materials from pulling apart. Think of inserting a hitch pin through the hole in your vehicle’s hitch receiver, passing through the hitch’s identical holes inside, locking the hitch in place. A pin is often used in an interference fit, being installed with a pressing or tapping tool to seat them.
Here we’ll describe the most common pin-style fasteners:
- Dowel Pin – the most common pin variety, a dowel pin is a solid, round rod used mostly to align or pivot two parts. Dowels are available in a wide array of designs, such as threaded ends, vented, grooved, knurled, round headed, barbed, and tapered.
- Removable Dowel Pins – adding more features to the above standard dowels, removable dowels add a host of handles, quick-release spring buttons, ring caps, knobs, locking clips, and levers to the mix. Some even feature expanding diameters, where flipping an end-handle expands the pin diameter for a tight, vibration-resistant fit.
- Hollow Dowel Pins – these variants of standard solid dowels provide a few application-specific benefits. Hollow cylinder dowels offer lower weight, a space to run wiring or tubing through, and compound holding tension via split, coiled, and spring types
- Cotter Pins – a standard cotter pin consists of two prongs that are inserted through a hole, where one prong can then be bent up to retain the pin in place. From there, a wide selection of cotter pins exists where one prong provides the shear retention mechanism, and the other prong encapsulates, clips over, coils around, or snaps across the shaft being pinned in order to secure the cotter.
There are certainly more pin styles available than we can describe here. Clevis pins, snap pins, loop pins, button pins, on and on. All pins have the same function – slide through a pair of orifices in separate materials, and hold the components together by maintaining the alignment of the orifices. All of your usual material types are available for pins: plated steel, carbon steel, stainless steel, aluminum, plastics, and even wood.
Specifying pins can be slightly challenging, between selecting materials, fit tolerances, shear strengths, and style options. E&T Fasteners offers expert opinions on these types of questions and more, helping you select the correct solution for your needs. Contact us to discuss your special application, or to see our standard fastener offerings, visit our product selection here.
Clip-Style Retention Fasteners
Clip-style fasteners are the natural counterpart to pin-style fasteners, on account of how they function. Where a pin is installed ‘through’ a fixture to secure it, a clip is installed ‘around’ a fixture to secure it. In the same way that a paperclip or hairclip works, a clip fastener attaches itself via an external binding force. Some clips are employed to bind groups of materials together, and other clips are utilized to retain fixtures from traveling apart.
Here are several examples of clip fasteners:
- Hairpin Clips – this clip snaps around a cylindrical shaft, usually into a machined groove, keeping the shaft from sliding out of its fixture during use. The clip acts as a ‘bumper’, limiting travel parallel to the centerline of the shaft.
- Retaining Ring Clip – similar in function as a hairpin clip, the retaining ring clips externally around a shaft or internally within a hollow shaft to limit travel out of the fixture. A ring clip usually needs a special tool to install or remove. We’ll have a future separate article all about retaining clips to dive deeper.
- Hitch Pin Clip – mostly used to hold pin shafts on your vehicle’s tow hitch, the hitch pin clip utilizes one straight prong and one bent prong to snap over the end of the pin, creating tension to hold the pin in place.
- Crescent Ring Clip – a variant of the standard ring clip, a crescent ring typically addresses special application parameters in its design, such as having a particular shaft coverage circumference less than 360 degrees, a wider or tapered profile, or a longer overall length.
With the above examples, we’ve only focused on clip fasteners that function in a shear-retention fashion. The term ‘clip’ is quite generic in common use, and can refer to a much wider selection of hardware solutions. In an upcoming article, we’ll cover two other categories of hardware where clips are often found: wire and cable hardware.
Retaining clips are most often found in metallic materials, given that their uses are typically in industrial motion and power, automotive, and high-speed equipment application. Plastic materials are available, usually limited to toy, consumer electronic, household appliance, and other light-duty uses.
E&T Fasteners is here to help you navigate fastener options to best meet your application and project needs. Price quotes, availability, lead times, delivery confirmations, unique application suggestions – whatever your need, we’re here to take your call or email. For support and advice from our fully trained staff, speak with an E&T sales representative today.
About E&T Fasteners
With sales and support teams spanning the Continental US, E&T Fasteners is here to serve your hardware, fastening, and component needs both domestically and internationally. We are a stocking distributor of metallic, plastic, and exotic alloy fasteners, backed by our technical staff directly experienced in your unique applications. We can assist your specifying and selection efforts, providing engineered solutions, record-fast lead times, and stellar customer service from quote through delivery. Please let us know how we can help!