The becket holds the end of the rope under the cleat to allow rigging with a 2:1 advantage. Alternatively, the becket can hold shockcord & bungee.  No need for extra parts. Ideal for Cunningham adjustment.  Use as a deck cleat or fit onto masts, booms and curved surfaces.  On the photo of a CL704AN on a Tasar boom, note the sealant used between the cleat and boom, to avoid corrosion.