surfaces 18a of the end portions of the ratchet 18 opposed to the end faces of the main body of the bracket 16 and said recesses 18f are filled with the lubricant 60 of high viscosity such as the sound arresting grease since the other arrangements are similar to the aforesaid conventional example and functions are similar to the aforesaid thirteenth embodiment explanations thereof are omitted in addition the recesses 18f in the aforesaid fourteenth embodiment are formed by cutting away portions of the shock receiving surfaces 18a of the ratchet 18 but the method of forming the recesses 18f is not limited to the above and it is of course possible to form said recesses 18f into grooves as in the fifteenth embodiment shown in fig3 to form said recesses into a multiplicity of small recesses as in the sixteenth embodiment shown in fig3 or to form said recesses into tapered cutouts formed on the side surfaces of the shock receiving surfaces as in the seventeenth embodiment shown in fig3 and 37 the eighteenth embodiment of the present invention is shown in fig3 and 39 in this embodiment recesses 16g are formed on shock receiving surfaces 16a of the bracket 16 opposed to the ratchet 18 and guiding projections each formed at its end face with a recess 62b are formed at shock receiving surfaces 18a of the ratchet 18 opposed to the bracket 16 since the other points are similar to the aforesaid conventional example explanation thereof is omitted in this embodiment when the end portions of the main body of the bracket 16 and the end portions of the ratchet 18 are brought into abutting contact with each other the guiding projections 62 project into.