Coaxial Cable & Adapter Accessories Roundup: Spring Loaded, Adapter Bullets, Full Detent, & Open Circuit Connector Caps

There is a wide variety of different coaxial transmission line hardware types and configurations. Hence, there are a wide range of accessories to go with these various coaxial connector, adapter, cable, and assembly arrangements. This blog covers a quick overview of a few of this, namely SMPS adapters with features such as spring loading, adapter bullets, and full detents, as well as BNC open circuit connector caps. Examples of these accessories include SMPS Spring Loaded Adapter, SMPS Female Adapter Bullet, SMPS Full Detent to 1.85 mm Adapter, and BNC Male Open Circuit Connector Cap.

Spring Loaded Adapters

Typical coaxial adapters are screw types that may be male or female and of one or more coaxial connector types. In the case of spring-loaded adapters, these adapters are not usually of the screw type coaxial connector and are instead usually of the blind-mate or push-connect type. The spring loaded allows for some tolerance in motion along the direction of the adapter while still maintaining a mechanical and electrical connection with the matching coaxial connector. Without the spring force holding the connection, in some applications, shock or vibration could eventually allow for the connection to lose or disconnect entirely.

Key Takeaways 

• Spring-loaded adapters provide tolerance for motion and vibration by maintaining connection pressure, reducing the risk of accidental disconnects.  

• Adapter bullets are ultra-low-profile; cylindrical in-line coaxial adapters used where space is limited, or minimal interruption is required.  

• Full-detent adapters (versus limited detent or smooth bore) provide higher insertion/withdrawal force, improving mechanical stability for critical or vibration-prone connections.  

• Open-circuit connector caps are used to safely terminate unused ports when a matched load isn’t required 

• protecting the port from contamination, damage, or unintended connection.  

• Choosing the right accessory improves system reliability, especially in high-frequency, high-density, or rugged environments where standard adapters may degrade performance. 

Coaxial Bullet Adapters

Bullet adapters are simply round coaxial adapters with minimal material and profile and typically of the same coaxial connector type. The term “bullet” is used to describe many cylindrical and simple in-line connector types throughout the electronics industry.

Full Detent Adapters

There are three levels of detents specified for SMP, and hence SMPS, connector types in MIL-STD-348, the full detent, limited detent, and smooth bore. The full detent is used to provide the highest level of insertion and withdrawal forces, followed by the limited detent and then the smooth bore. Full detents are used when the cable withdrawal forces need to be high, such as with cable assembly applications or when a connection needs to withstand significant shock and vibration and concern of damaging the connected electronics with a high withdrawal force isn’t a primary concern.

Open Circuit Connector Caps

Where most coaxial terminations are typically matched loads, this is not always the case. There are also open circuit and closed-circuit connector caps or terminators. It is less common to call open circuit or closed-circuit caps terminations or loads, though this is technically correct, as that might create confusion with matched terminations/loads. In many cases open or closed-circuit terminations are specifically chosen for this purpose as the circuitry connected to the external port requiring the cap is best connected as an open circuit or closed circuit instead of a matched load.

Recommendations 

• Use spring-loaded adapters in mobile, avionics, or test-bench setups where mating/un-mating and vibration are frequent.
   

• Deploy adapter bullets when you need minimal profile and a stable connection through dense rack systems or tight mechanical fits.
   

• Where connections are subject to mechanical shock or cable strain, specify full-detent adapters to enhance retention and avoid inadvertent disconnects.
   

• Protect spare or unused connectors with open-circuit caps to avoid dust ingress, moisture, or accidental contact affecting system calibration or integrity.
   

• Maintain inventory of these accessory types to match the mechanical, environmental, and signal-integrity needs of your RF/coaxial infrastructure.