Casing Head (or Braden Head)
A heavy steel fitting connected to the uppermost end of the surface casing. It provides a pressure seal for subsequent casing strings placed in the well and allows suspension of intermediate casing strings and the production casing. It also provides outlets to release any pressure that might accumulate between casing strings. The casing head is usually connected to the surface casing by a threaded connection, but in deep wells it may be attached by welding.
Source: API BULLETIN E3, Environmental Guidance Document: Well Abandonment and Inactive Well Practices for U.S. Exploration and Production Operations, First Edition, January 1993 (Reaffirmed June 2000). Global Standards