this is a listing for One BNC Male bulk head flange RF connector socket.

Beware of foreign cheap imitations that drop to bits or fail - 

What you get here is a quality product UK Made to NATO military specification, Brass nickel plated with gold centre pin. it has 4 holes to allow fixing to surface. Fixing centres are 13mm apart.

The dimensions are as per photos showing tape measure.

The centre pin is a solder pot, allowing easy connection to either a PCB or coax inner.