This is an old fashioned ventilating sash lock unfamiliar to many.
Shown in the unlocked position above, this allows the sash to be operated freely without restrictions.
This lock is usually installed as a supplementary lock to allow the window to be opened to a certain point but no further.
See below for more photos.
Fashioned from cast iron with a dark clear-coated finish.
Size: 2-1/2" long x 3/16" thick.
Provided with 2 screws.