You have asked for information on the CONSTRUCTION MECHANIC rating. The rating symbol is an Open Ended Wrench atop a Hex Nut
The U.S. Navy is made up of four distinct groups of technical rating specialist. These categories are:
Administrative and Medical
Aviation
Hull
Construction
The term SEABEE was originally coined to define the Naval combat construction forces assigned to the Naval Civil Engineering Corps, and the SEABEES became a recognized organization in 1942. The traditional SEABEE specialty ratings are made up of seven classifications shown as the top left seven on the home page. As SEABEES tend to be self sufficient in a combat zone or other deployed area, other ratings are assigned to the SEABEES to provide the skills necessary to accomplish this.
While any rating within the U.S. Navy can be billeted with a SEABEE group depending upon the nature of the task at hand, the home page includes thirteen typical other ratings that were most assigned to be part of a SEABEE unit during the Vietnam Era.

Construction Mechanic (CM):
CMs maintain heavy construction and automotive equipment - buses, dump trucks, bulldozers, rollers, cranes, backhoes, pile drivers - other construction equipment and service vehicles. They work on gasoline and diesel engines, ignition and fuel systems, transmissions, electrical systems and hydraulic, pneumatic and steering systems.