Beryllium-Copper (BeCu) is a very common material used in the manufacturing of coaxial connectors and adapters, particularly as the base material for the centre Pin or Socket. There are several reasons why BeCu is often the material of choice for these applications.

First, BeCu has excellent electrical conductivity, similar to brass, which makes it well suited for transferring high-frequency signals with minimal losses or distortions. BeCu also has a higher tensile strength compared to brass, which makes it more suitable for high-power applications where high current loads are expected. This higher strength also makes BeCu more resistant to deformation and wear over time, which can help to ensure reliable performance even in harsh operating environments.

Second, BeCu is highly resistant to corrosion and oxidation, which is important in applications where the connectors and adapters may be exposed to moisture or other corrosive substances. This property helps to ensure that the electrical contacts will maintain their performance over time and will not degrade due to environmental exposure.

In addition to its electrical and mechanical properties, BeCu is also relatively easy to machine and fabricate, similar to brass, which makes it well suited for producing connectors and adapters that require precise tolerances and intricate shapes. However, Beryllium-Copper (BeCu) is more expensive than brass which leads it to often only used in the most important component(s) within the connector. This is because BeCu is a more specialised and high-performance material and the production process for BeCu is more complex and costly.

Despite the higher cost, BeCu is often used in applications where high electrical and mechanical performance are critical as it has superior properties compared to brass in these areas. The higher cost is often justified by the improved performance and reliability that BeCu can provide, particularly in high-power and repeated mating applications.