The 1.85mm was designed to go beyond the SMA interface constraints, and as a result is NOT SMA compatible. Instead, maximum performance to the highest possible frequency that the geometry would allow, along with repeatable measurements after hundreds or even thousands of interconnects, were the design goals. The connector outer conductor ID is 1.85 mm, and OD is 4.7 mm, allowing compatibility, so that the 1.85mm connector mates with the 2.4mm connector and has the same ruggedness. It’s a 50 Ohms connector with performance up to 67 GHz.