The Shepherd's Crook Fastener is cast and then annealed and is reversible (not handed) so can be fitted to either the left or the right side of the window.
It is also suitable for the use on windows that have a draft seal.
For windows without a central mullion, use with a hook plate 33237. See below for link.
Fixing Plate: 2 3/8 x 3/4 (60mm x 19mm)
Mortice Plate: 3 x 3/4 (76mm x 19mm)