Try this oval-shaped curtain rod when you want to mount curtains inside of the window frame. The spring allows you to adjust the length of the rod without having to add any holes to your walls.

For mounting window treatments inside a window frame
No mounting hardware required
5/8" wide
Steel/plastic. 

Included: 1 Set of Mounting Hardware
Features: Adjustable
Use: Indoor
Rod Diameter: 5/8"
Base Material: 98% Steel, 2% Plastic
Curtain Rod Length: Under 28in
Care: Wipe Clean
Country of Origin: Imported