A king pin coupling (for example in a helicopter control linkage) comprises a tubular king pin 16 extending between bearings 8, 10 provided in respective limbs of a fork 4. A safety bolt 22 extends coaxially through the king pin 16 and engages a bearing 10 with a screw-threaded end 36. Tightening of the bolt 22 by its screw-threaded end 36 into the bearing 10 causes a collar 42 to act against a stop ring 46 to load the king pin 16 by its end 48 against shoulder 50 and lock the pin against axial movement. A safety mechanism preventing unintentional unscrewing of the bolt 22 is provided and in the construction shown comprises a sleeve 26 axially slidable but rotationally fast on the bolt 22, this sleeve being loaded by a spring 34 so that teeth 54 thereon interengage with complementary teeth 56 on the bearing 8. <IMAGE>
