The Columbia Series 300 aluminum basement window is a single glazed aluminum basement insert. 

Size: 31 x 12-5/8
Has two (2) metal spring clips slide at top of 3/4 inch thick frame.

The Columbia Series 300 aluminum basement window is a single glazed aluminum basement insert. 
Maintenance free, energy efficient. 
Easy, 1 minute installation.
Requires no tools for installation; uses high tensile steel spring clips to secure the insert in the opening.

Color: Aluminum finish standard, 

Adjustable window sash lock will also slide up and down.

Replaces Columbia, Monarch and Kewanee single-pane basement windows. 

Standard Sizes
31 x 12-5/8
31 x 16-5/8
31 x 20-5/8
31 x 36-5/8 

Priced and sold each.

Resources: 
Article: How to Replace Basement Window Inserts
Video: How to Replace Basement Window Inserts