Yep! It's a SO239 or "M" type connector.
Also named "UHF" connector althrough they are not the best connectors for the UHF band. (N-type connectors are much better for UHF up through 18 GHz)
Both electrically and mechanically, it is a rugged connector. However, you must get sure that the connector is well tightened. If it comes just a little loose, you'll get SERIOUS RF leakege problems !
By the way, i'm more attracted by the whole unit in the photograph rather than the SO239. What is it ?