PURPOSE: To change a king pin without removing a lower side cap by forming internal thread which is provided on the lower side cap of a king pin cap construction and screwed in with a grease nipple, into the parallel thread.

CONSTITUTION: In case of interchange or removing of a king pin 4, a lock bolt 9 fixing the king pin 4 is removed from an axle beam 3, an upper side cap 6 is removed from the upper part of the hollow part 1c of the upper side part 1a of a knuckle 1, a grease nipple 8 is removed from the internal thread 7a of a lower side cap 7, a bolt 12 is screwed in the internal thread 7a, the extreme end is contacted with the lower end of the king pin 4 to push up it, and the king pin 4 is taken out from the through holes of the knuckle 1 and the axle beam 3. In case of fitting the new king pin 4 to the through holes, previously the extreme position of the bolt 12 is moved near to the optimum supporting position, the king pin is inserted, and the bolt 12 is rotated to finely adjust the position of the king pin 4.