From The Anvil. Beeswax Monkeytail Fastener

The Monkeytail fastener is forged from steel, is reversible (not handed) and can therefore be fitted to either the left or the right side of the window. It is suitable for use on windows that have a draft seal due to the mortice plate allowing the window to be pulled as tight to the frame as the seal allows. For windows without a central mullion the Hook Plate must be ordered separately Suitable for internal use or when in areas with high moisture care and maintenance guides must be followed fairly regularly. Sold as a set with matching fixings. Finished in Beeswax.