Abstract: A sub-assembly of external parts including, coaxially with a first component and a second component compressing together a sealing and friction joint, and interposed therebetween, a bolt securing them together by axially blocking the first component, and a lower surface of which lies, in the assembled position, in the vicinity of an upper surface of the second component, which bolt includes a lower relief protruding axially from this lower surface towards the second component, arranged to either complementarily cooperate with an oblong groove which is partially of revolution that the upper surface includes, and interrupted by a stopper limiting the angular travel between the second component and the bolt within a turn, or else to constitute an angular stopper to an upper relief protruding from the upper surface of the second component and extending axially towards the bolt.