0.4/2.5 

0.4/2.5 & 0.4/2.8 are some of  the smallest true 75 or 50 ohm connector available.  This micro-miniature series is ideal for High Definition camera and CCTV applications or anywhere that a very small  board connection is required.  Suitable for use up to 3GHz, this series exceeds the requirements of SMPTE 292M / HD-SDI specification for HD broadcasts.

For details; http://www.coax-connectors.com/products/connectors/0425.aspx