This is an Encore series single arm crank operator used to open and close casement windows.
The manufacturer (Truth Hardware) calls this operator left handed: The handing is determined by the side the hinge is on when viewed from the outside. See SWISCO product 39-475 for the opposite handed version.
11/32" spline; handle and cover sold separately.
Mounts to sill
7-1/2" long stainless steel arm.
This replacement operating system is used by several window manufacturers; specially designed for coastal applications.