A fastener assembly contains: a first disc with a plurality of tip teeth, an engaging cylinder, a second disc, a retaining element, and a third disc. The engaging cylinder includes a first engagement structure formed on an inner wall thereof, and the engaging cylinder is connected with the first disc to form a main fastener. The second disc includes a through hole defined on a central position thereof and plural recesses radially extending from a peripheral side of the through hole, wherein the engaging cylinder inserts through and retains with the through hole of the second disc so that the engaging cylinder engages with the second disc. The retaining element is cylindrical or columnar and includes a second engagement structure arranged on a first end thereof, wherein a second end of the retaining element is coupled with the third disc to form an auxiliary fastener.