Socket unit with a rotating cover with three slots and a central protruding unit with a spring

A socket unit, comprising:

• a main body, having a circular indented region, which is provided with three first slots, wherein a hole is centrally provided in the circular indented region and the hole has an arc-shaped position-limiting slot and a positioning hole;
• a rotational cover, having three second slots and, whose sizes are slightly larger than or substantially equal to the first slots of the main body, wherein a protruding unit is centrally provided on bottom surface of the rotational cover, a cone-shaped connective portion is provided on inner end of the protruding unit and a sliding portion is disposed near outer end of the protruding unit;
• and
• a spring, wherein either end of the spring has a connective portion and wherein the spring is fitted onto the protruding unit of the rotational cover so that outer connective portion of the spring may be secured in the rotational cover,
• whereby, in assembly, the protruding unit is inserted into the hole of the indented region so that the cone-shaped connective portion may engage with the inner wall of the hole, wherein the rotational cover rotates around the protruding unit to line up with the three second slots of the rotational cover with the three first slots of the main body.