of the cotter pins illustrated in fig9 to 15 of the drawings its stop forming transverse stud 2009 is disposed behind an extension 2004a of ring 2004 beyond the pivot forming axis 2005 thereof said stud 2009 having if desired the structure of any one of the studs illustrated in fig9 to 15 in the exemplary form of embodiment shown in fig1 the stud 3009 instead of passing through the head 3002 of cotter pin 3001 extends in front of this head and is carried by a pair of lateral links 3021 pivoted to said head 3002 by means of a transverse pin 3020 so that the stud 3009 can be placed in front of ring 3004 and kept in its closed position in which it engages the pin body 3003 or above the head 3002 to permit the opening of said ring moreover a return spring 3021a is associated with the links 3021 for urging same in the direction to hold the ring 3004 in contrast with the examples illustrated in fig4 to 17 of the drawings fig1 shows a cotter pin 4001 corresponding to the pin illustrated in fig3 in fact the head 4002 of this cotter pin is provided with a transverse stud 4009 secured to this head and extending in front of the end portion 4004a of ring 4004 so as to be somewhat spaced therefrom to limit the permissible opening of ring 4004 to an angle of about 15 u00b0 to 30 u00b0 the stud 4009 is screw threaded and carries a wedge member 4016 adapted to be screwed in or out along said stud 4009 and disposed inside or outside of the gap left between the end portion 4004a of ring 4004.