as shown in fig3 the laminar component blank is in the form of two approximately triangular portions 17 connected by a reduced bridge section 19 so that when folded into u shape at the bridge section 19 the two portions 17 lie substantially parallel with each other at a distance corresponding approximately with the diameter of the section of the toroidal ring 1 the two portions 17 end with slightly concave opposing edges 21 designed to match the curvature of the ring 1 at opposite sides thereof the laminar portions close to the edges 21 may be slightly distorted by means of arched impressions to stabilise the relative positions of the component 15 and the ring 1 by slight elastic deformation and thereby with a slight pressure of the two portions 17 upon the ring 1 the assembly is then soldered or welded by means of easy operations adopted conventionally in the gold working trade so as to ensure a completely rigid assembly the position of the lug 5 must be directed with a slight slope in relation to the opening 1a of the ring 1 the movement of the catch 3 being such as that indicated by the arrow f3 against the loading of the resisting spring when opening the projection 3a can pass partly between the two laminar portions 17 formed by the component 15 the lug 5 consequently does not present an obstacle to opening operations the two portions 17 defining the two opposite faces of the lug 5 may have respective lips 23 which are folded back to meet closely along a side edge of the lug 5 opposite to the catch in.