2.4 mm connector
2.4 mm connectors are precision coaxial microwave connectors that look similar to SMA connectors but use air dielectric and work at higher frequencies than SMA, up to 50 GHz. The applicable standard is IEC 61169-40. Impedance is 50 Ω.
The 2.4 mm connectors are mechanically compatible with 1.8 mm connectors, but will not thread onto an SMA, 3.5 mm or 2.92 mm connector. This is on purpose, to avoid mixing these expensive connectors in with less precise connectors such as SMA and causing them irreparable harm in the process.
See also 2.92 mm connector, 3.5 mm connector.