Abstract: A trailer fastening device has a fastening shaft, a collar, a spring, and a solid ball. The collar has a center hole, a through hole, and an inner recess hole receiving the spring and the solid ball. The fastening shaft has a middle blocking disk, a lower threaded rod disposed on a bottom of the middle blocking disk, and an upper rod disposed on a top portion of the middle blocking disk. The upper rod has a helical groove, a blind hole formed on an end of the helical groove, and the end of the helical groove being a bevel. The upper rod is inserted in the center hole of the collar. The collar is rotated until the solid ball reaches the blind hole of the upper rod.

Abstract: An engine has a drive shaft fastening a first sprocket wheel. A transmission gear box is disposed on a vehicle frame. The transmission gear box has a driven shaft fastening a second sprocket wheel. A chain surrounds the first sprocket wheel and the second sprocket wheel. A hexagonal nut is disposed on the driven shaft. A milometer device is disposed on the driven shaft. The drive shaft is disposed on a transmission gear box. A bolt fastens the milometer device and the hexagonal nut together.

Abstract: A transmission mechanism has an outer casing. A hollow tube is connected to a bottom of the outer casing. A main frame has a panel having a round aperture. A shock absorbing assembly has a buffer device, a positioning seat disposed on the buffer device, and a screw rod fastening the positioning seat and the hollow tube together.