Patent ID: 8011526

Claim:
A loosening prevention device for a plug, the loosening prevention device comprising: a first sleeve engaged with and surrounding a first plug attached to a lid of a liquid tank, the first sleeve having an inner diameter; a second sleeve engaged with and surrounding a second plug attached to the lid; a third sleeve integral and coaxial with the first sleeve and having an inner diameter larger than the inner diameter of the first sleeve wherein the third sleeve is engaged with and surrounds a socket connected to the first plug; at least one key or keyway extending in an axial direction is formed on an outer circumferential surface of the socket, and at least one keyway or key engaged with the at least one key or keyway of the socket is formed on an inner circumferential surface of the third sleeve; a connection means for connecting and fixing the first sleeve and the second sleeve with each other, wherein at least one flat surface is formed on an outer circumferential surface of both or either one of the first plug and the second plug, and at least one flat surface in surface contact with the flat surface of both or either one of the first plug and the second plug is formed on an inner circumferential surface of both or either one of the first sleeve and the second sleeve.