F Type 

F type are low cost 50 & 75 ohm miniature connectors typically used in cable TV, satellite TV, CATV  and cable modem installations.  F type have a screw coupling and commonly use the solid centre conductor of the cable as the centre contact although versions with a loose contact are available.

For details; http://www.coax-connectors.com/products/connectors/f-type.aspx