What's different about SMA 2.4 and 3.5mm?

I think that type of used cable only.

Connectors with names in mm are improved versions of older connectors and also new type connectors. They have less of an impedance bump than the older ones and operate at higher frequencies.

In some cases, they will mate with older connectors with reduced performance.

The name of the connector is 2.4mm not sma 2.4.

The name comes from the inner diameter of the outer conductror of the coax.
Less is the diameter, greater the working frequency of the connector.

2.4mm --> 50GHz
3.5mm --> 26GHz or (precision 3.5mm) 34 GHz.


Read also http://www.elektroda.pl/eboard/viewtopic.php?t=55293.