The invention relates to a cap. More particularly, the invention relates to a bottle cap which has engaging formations which allow it to be releasably secured to other caps of the same kind. The cap includes a sleeve moulded integrally to an end wall, the sleeve having at least one line of weakness spaced apart from the end wall for separation of at least one ring portion from the sleeve. The cap further includes primary external co-operating engaging formations provided on either side of the line of weakness, such that the cap is connectible side-to-side, via the primary external cooperating engaging formations, to other caps or ring portions, or to bottles having corresponding primary external cooperating engaging formations.