This is an old fashioned ventilating sash lock unfamiliar to many. For a video of its operation click here.
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.