Table of Contents


      Keyhole Standoffs
      Snap-Top Standoffs
      Floating Nuts
      Blind Nuts
      Flush Nuts
      Locking Nuts
      Rivet Nuts
      Locating Pins
   Captivated Screws
      Simple Screws
      Spring-Loaded Screws
      Knob Cap Screws
   Threaded Inserts
      Press-In Inserts
      Molded-In Inserts
      Ultrasonic/Heat-Staking Inserts
      Compression Limiters
   Specialty Fasteners
      Cable Tie Mounts
      Tack Pins
      Panel-to-Panel Fasteners
      Right Angle Fasteners

Attachment Technologies

   Surface Mounting

Standoffs are a versatile family of fasteners meant to hold a fixed gap between two panels via some static attachment. They are made from rigid bar stock in round, hex, and sometimes square profiles based on the requirements of the application. A standoff with a male attachment has external threads like a screw or bolt, while a female attachment has internal threads like a nut. Either end of a standoff can be male, female, or a combination of any of the available attachment technologies. Some can forego threads for snap-top or keyhole features to solve more specific application problems.

A common application for standoffs is the mounting of PCBs to manage potential short circuits. The housing of a gaming PC is essentially a large, current-carrying metal box, and raising the motherboard away from the housing helps to eliminate the risk of a short circuit between components. Additionally, the use of brass or steel standoffs serve as a connection to ground in the case of some large electrical discharge, directing it away from more delicate circuitry. The gap also helps with heat transfer via airflow while remaining rigid for sprawling electrical connections.

Some prebuilt PCs have integrated standoffs or “nubs” designed into the housing to minimize the number of loose parts. While this may be cost effective for a mass produced assembly, it limits the potential for customization using upgraded components. For custom PCs, it wouldn’t make sense to develop several cases with standoff nubs in every possible location for different components, but instead use fasteners that allow for more freedom of placement.

On the manufacturing side, if a company had several models of prebuilt PCs, greater placement flexibility can be achieved by using self-clinching standoffs rather than welded nubs. This can decrease tooling or assembly costs and facilitate production modifications for new designs. Broaching or surface mounted (SMT) standoffs are used for spacing an additional panel or component above a circuit board in a PCB-to-PCB junction. However, the most common standoffs for PCB mounting in telecom or datacom applications (also known as “super screws”) are a male-female thread combination made from hexagonal bar stock. The hex body can be torqued to tighten the standoff into a panel, while the internal thread on the opposite end can receive a screw to retain a PCB.

Keyhole Standoffs

Keyhole standoffs have a unique attachment feature on the top end of the body. The common design includes a retaining disk atop a narrow column, which sits on a shoulder that is slightly larger in diameter than the disk. The opposite side of the fastener can still employ a variety of attachment technologies as the keyhole design is rotationally symmetric and doesn’t experience torque in application. Given no requirement to resist torque, round bar stock is the most common bar for keyhole standoffs.

The word “keyhole” comes from the shape of the hole in the panel (usually a PCB) that resembles a keyhole in a door; a circular hole with one protruding cut. The diameter of the hole accepts the retaining disk and sits on the shoulder, while the width of the cut straddles the column as the PCB is slid into place. For simplified disassembly, a PCB can have three corners supported by keyhole standoffs while a threaded standoff supports the last corner. This way, only one screw is needed to secure all three axes of movement.

Using the same application, all four corners could be supported with threaded standoffs to minimize part variety, but the time associated with threading and unthreading all four connections makes for less convenient assembly. The combination of keyholes and threaded standoffs can speed up production assembly while facilitating repeated disassembly. However, strictly using keyhole standoffs will not be able to fully secure a PCB due to the movement required for assembly.

Like regular threaded standoffs, keyhole standoffs can be attached to panels through several self-clinching methods depending on the requirements of the application. Additionally, they can be installed into PCBs via broaching or surface mount technology (SMT) for stacks of multiple layers of panels or components.

Snap-Top Standoffs

Snap-top standoffs have a unique attachment feature on the top end of the body. A roughly spherical retaining geometry sits on a shoulder below which the diameter slims for a short distance before returning to the barrel diameter of the opposite end of the body. Additionally, two perpendicular cuts centered along the axis travel the length of the slim diameter, allowing for the four quarters to deflect inward and creating a flexible outer diameter approaching the tip of the retainer. The opposite side of the fastener can still employ a wide variety of attachment technologies as the snap-top design is rotationally symmetric and doesn’t experience torque in application. This symmetry also commonly results in the use of round bar stock.

The snap-top standoff can eliminate the use of screws in panel or PCB mounting via a vertically displaced interference fit. The holes in a PCB are machined slightly smaller than the outer diameter of the retaining geometry at the top of the fastener. With some force, pressing the PCB over the retainer causes the reduction of the outer diameter via deflection. Once the PCB passes over the widest diameter, the deflection of the quarter sections presses the board into the shoulder, retaining it. A fully rounded retaining geometry will allow for easy disassembly, while a ramp-and-shoulder style retainer is more secure.

If the goal of the application is to eliminate loose hardware, a potential alternative would be an array of keyhole standoffs. The unrestricted movement in one linear direction could be traded for a rotational displacement, like a smoke alarm fixture in a house. However, whether rotationally or linearly installed, PCBs positioned with keyhole standoffs always require some movement in-plane with the panel or PCB, requiring more room in the assembly as well as being susceptible to shifting or rattling. Snap-top standoffs can circumvent this due to their vertical installation, requiring only enough room to get a tool under the board to pull it off of the snap-tops. However, there may be some instability without a distinct shoulder in the retainer when compared to threaded standoffs paired with a screw.

Due to their utility in PCB applications, snap-tops commonly use self-clinching for panel-to-PCB joints or surface mounted technology (SMT) for PCB-to-PCB stacks. Broaching snap-top standoffs are rare due to the force involved with assembly and disassembly, as it could weaken the interference fit between the broaching geometry and the brittle PCB over multiple loading cycles.

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Your resource for applications-first discussions of fasteners made for consumer & commercial products. Planes, cars, phones & medical devices all have many components that need to be held securely together, but how this is achieved is often difficult to access due to proprietary product information protected by the vendor. Here, we’ve provided examples of fastener applications without affiliations to demonstrate how and why specific fasteners are implemented to solve a variety of assembly problems.

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