K B Corporation

A "friction stay" is a type of hinge used on windows, particularly casement windows, that provides controlled opening and closing by applying adjustable friction, allowing the window to stay open at various angles while still providing secure closure; essentially, it's a hinge with a mechanism that creates resistance to prevent the window from slamming shut or opening too far, holding it in position at different angles. 
Key points about friction stays:
Function:
They allow for smooth and controlled opening and closing of windows by providing resistance through a friction mechanism. 
Adjustable:
Most friction stays have an adjustable feature to fine-tune the level of resistance needed based on the window weight and desired opening angle. 
Safety feature:
By preventing windows from slamming shut, friction stays can be considered a safety feature, especially for children and pets. 
Common usage:
Often found on casement windows, where the window swings outward.