Attachment device with improved openable swivel

A swivel attachment device comprising:

• a pair of rings able to rotate freely with respect to one another around an axis of rotation formed by a central pivot-pin,
• at least one of the rings being in the form of a hook delineating a lateral access space,
• a closing part designed to close said space performing partial take-up of the tractive forces, said closing part comprising a removable fixing screw being laterally spaced apart from the axis of rotation, and extending in a substantially parallel direction to the central pivot-pin in the closed state,
• said closing part comprising a spacer through which said fixing screw passes, said spacer pressing on two opposite surfaces of the hook, and
• one of the rings having a hollow base comprising an annular positioning surface cooperating with a rim of the other ring leaving a predefined clearance for free rotation of the rings around the central pivot-pin, wherein the base of the ring is provided with a housing for receipt of a bearing, which is inserted between the head of the pivot-pin and the rim of the other ring, the bearing and the pivot-pin being configured to leave a clearance between the pair of rings.