How to Choose the Right VPX Ejector Handle

This guide covers how to select the right ejector handle for VPX and VME board designs. It walks through WaveTherm's three ejector handle families, standard 3U, Hex Key, and Variable Force, and the key selection variables: form factor, retention requirements, mechanical advantage, standoff height, and finish.

3U vs. 6U: How Form Factor Affects Your Options

6U boards have significantly more card width available, which allows for longer ejector handles and higher mechanical advantage. 3U boards are physically narrower, and that constraint limits how much leverage you can build into the handle design. If you need high mechanical advantage on a 3U board, your options are more limited simply because there is less room for a longer lever arm.

For 6U boards, WaveTherm's Hex Key Ejectors are the primary retained option. For 6U designs where retention is not required but maximum insertion and ejection force is, a longer standard handle like the 14306 takes advantage of the available card width to deliver higher mechanical advantage. For 3U, the standard ejector handle family covers most applications, with Variable Force Ejectors the right choice when the design follows VITA 78.0 or a similar standard that calls for controlled, tolerance-compensating insertion force.

Standard vs. Retained Ejectors: The First Decision

Standard ejectors move freely in the slot. They are not mechanically locked to the card or heatframe. They provide leverage during insertion and extraction but are only constrained by the chassis walls once the card is seated and the wedgelock is holding the card in place. This is the simplest and most common configuration for 3U boards, where constrained card width also makes fitting a retained ejector more difficult.

Retained ejectors have a mechanical means of staying locked to the card assembly. WaveTherm offers two retained ejector families: Hex Key Ejectors and Variable Force Ejectors. Retention adds security in high-vibration environments and applications where loose hardware is a concern, but it is also important in liquid flow-through cooling applications. In those systems, the board needs to be locked in place before the wedgelock is expanded to ensure proper seating and sealing. A retained ejector provides that positive lock independently of the wedgelock.

Standard 3U Ejector Handles

WaveTherm's standard 3U ejector handles are available in universal and directional (left/right) orientations. Universal models are generally preferred. They can be installed on either side of the card without specifying orientation at procurement, which simplifies inventory and reduces the risk of ordering the wrong part.

Selecting Mechanical Advantage

WaveTherm's current 3U universal models range from about 2.6x to 3.3x mechanical advantage. The right choice depends primarily on your connector. Two factors drive the decision:

• Ejection travel: The handle needs enough travel to fully unseat the connector. Connectors with longer engagement depth require more ejection travel. If the handle cannot provide enough, the card will not pull free cleanly.
• Insertion and ejection force: Higher-pin-count and high-density connectors require more force to mate and unmate. Higher mechanical advantage multiplies the force you can apply at the card edge.

The 14104 provides the highest total ejection travel (0.252") among the standard VPX-compliant handles and is WaveTherm's top recommendation for most VPX applications. The 14283, with a slightly higher mechanical advantage (3.05x vs. 2.6x), is the recommended choice for PMC form factor applications where the mezzanine geometry requires it. If your connector has demanding force requirements and adequate travel, go with higher mechanical advantage. If connector travel is the tighter constraint, favor the 14104.

Browse WaveTherm's standard 3U ejector handle collection to compare model specifications side by side.

Hex Key Ejector Handles

Hex Key Ejectors (HKE) are WaveTherm's retained ejector solution primarily designed for 6U VPX boards. A captive hex drive screw locks the handle to the card frame, keeping it secured during operation and preventing movement during shock and vibration events.

One Tool for Wedgelocks and Ejectors

One practical advantage of the HKE design is screw size compatibility. The hex drive screw on the ejector handle can be specified to match the drive screw on the wedgelocks in the same system. When the screws match, a technician can loosen the wedgelocks, unlock the ejector handle, and extract the card using a single hex key. In field maintenance environments, that kind of simplification has real value.

Available screw sizes include 3/32", 7/64", and M2.5. Specify the size that matches your wedgelock drive screws at the time of ordering.

Selecting Handle Length

WaveTherm HKE handles come in two standard lengths: 1.62" and 1.97". The 1.97" handle is the recommended standard. The longer length provides better mechanical advantage and is the right choice in most 6U applications where chassis geometry does not restrict it. The 1.62" handle is available for tighter installations where the longer handle will not fit.

Captive Screw Length

HKE handles are available with two captive screw lengths: 5.75mm and 7mm. The 7mm screw is recommended when the heatframe has enough material to accept a full thread engagement. The 5.75mm screw is available for installations where limited heatframe thickness restricts how deep the thread can be tapped.

While Hex Key Ejectors are primarily designed for 6U boards, it is possible to use a single HKE on a 3U board in certain applications where a retained ejector is needed and chassis geometry allows it.

Browse WaveTherm's Hex Key Ejector collection for full configuration options including screw size, length, standoff, and finish.

Variable Force Ejector Handles

The Variable Force Ejector (VFE) is WaveTherm's most advanced ejector handle. It is the primary choice for VITA 78.0 (Space VPX) designs and applications that require consistent, controlled backplane engagement force across board insertion and removal cycles.

How Variable Force Works

The VFE uses a patented double-pivot, force-multiplying design with an internal spring. As the card is inserted, the spring flexes to compensate for slight variations in board tolerance, keeping force evenly distributed across the connector during mating. This protects connector pins and backplane receptacles from the damage caused by uneven or excessive insertion force. The same mechanism provides controlled resistance during extraction, so the connector unseats cleanly rather than coming free suddenly.

This tolerance-compensating behavior is particularly valuable in high-reliability applications where connector integrity must be maintained across many insertion and removal cycles.

VITA 78.0 Compliance and Retention Mechanism

The VFE is fully VITA 78.0 compliant and is also compatible with some VITA 48.4 and 48.5 configurations. It locks to a tab on the heatframe, a retention feature defined by the VITA 78.0 standard itself. If your design follows VITA 78.0, the VFE integrates into the heatframe as specified by the standard.

Mounting Hole and Rivet Size

The VFE is available in two mounting hole diameters: 0.06" and 0.09". Both sizes are defined in the VITA standard, and the rivet used to attach the ejector is sized to fit either hole. WaveTherm recommends the 0.09" configuration. The larger hole creates a stronger, more robust attachment that performs better in demanding environments. If you have flexibility at the design stage, spec the 0.09" version.

Browse WaveTherm's Variable Force Ejector collection for ordering details.

How to Select the Right Standoff Height

Standard and Hex Key ejector handles are available with standoff options to account for varying heatframe bore depths. The correct standoff height is determined by the bore in your heatframe, not by PCB thickness alone.

Available standoff heights are: 0.1875", 0.250", and 0.3125". The 0.250" standoff is WaveTherm's standard recommendation and covers the majority of heatframe configurations and VITA 48.X. If you are building to a standard WaveTherm OpenCOTS heatframe, start with 0.250" unless your design documentation specifies otherwise.

When ordering with a standoff selected, the handle ships with a complete hardware kit including the standoff, washer, and two different screw length options. No separate hardware order is needed. If you order with no standoff, the handle ships with no mounting hardware at all, so make sure you have the necessary fasteners on hand before ordering without a standoff.

Variable Force Ejectors do not use a standoff. They attach directly to the heatframe tab and do not require a standoff specification.

Recommended Finish Options

WaveTherm ejector handles are available in multiple surface finishes to meet program specifications and environmental requirements:

• Black Anodize (BA): Standard anodize finish. Low-reflectance, corrosion-resistant, and commonly specified across defense programs.
• Hard Black Anodize (BH): Harder and more wear-resistant than standard anodize. Better for high-cycle or abrasive environments.
• Electroless Nickel (EN): Uniform metallic coating with good hardness and corrosion resistance. Often specified for precision fit applications or specific mil-spec surface requirements.

Match your ejector finish to the finish used on the rest of your card assembly hardware for consistency and to meet any program-level surface treatment specifications.

Front I/O Considerations

If your card design includes front I/O, ejector handle profile becomes a real constraint. Connectors, cables, and panel features at the front of the card compete for the same space as the ejector handle. A handle that protrudes too far or sits too high can block access to front I/O or prevent proper cable routing.

Lower-profile ejector handles are preferable in front I/O applications, and this is especially pronounced on 3U boards where overall card width is already limited. On a 3U card with front I/O, ejector handle selection should factor in the clearance envelope early in the design process rather than as an afterthought.

Quick Selection Summary

If you are working through the decision for the first time, here is a simplified starting point:

• 3U board, standard VPX, no retention needed: 14104 for most VPX applications. 14283 for PMC form factor.
• 6U board, no retention needed, maximum insertion/ejection force: 14306.
• 6U board, retained ejector, shared tooling preferred: Hex Key Ejector, 1.97" length, hex size matched to your wedgelocks.
• VITA 78.0 design or tolerance compensation required: Variable Force Ejector, 0.09" hole with rivet preferred.

WaveTherm's engineering team is available for direct support on complex selections. All ejector handles are built to order and made in the USA.