Answer
Beryllium Copper (typically Alloy 25, UNS C17200) is used for spiral retaining rings in environments where non-sparking properties are required for safety (e.g., explosive atmospheres) or where non-magnetic properties are required (e.g., MRI machines or sensitive electronic equipment). CuBe is precipitation-hardened to achieve tensile strengths comparable to alloy steels (up to 1400 MPa). However, its modulus of elasticity $E$ is lower (approx. 131 GPa) compared to steel (200 GPa). This means a CuBe ring will have a lower radial grip for the same dimensions. Designers must compensate for this by increasing the interference fit. Additionally, CuBe has excellent electrical conductivity, making it useful as a ground path in some RF connector assemblies.
