These hooks are designed to be the interface or mount between a Duronic BPS projector screen (i.e., those that have a model number starting with the letters "BPS") and the metal retaining brackets that are fixed into a poptop and used to keep it closed.
The mounting hooks are the exact profile to fit over the top bar of a Duronic BPS screen and can be slid along the length of the bar so that they line up appropriately with the spacing of your poptop brackets.
Each set contains 2 hooks to match with a typical poptop configuration.
 
These may be compatible with other projector screens if the top bar is 20mm in diameter or less. Pictures shown are with the BPS40/43 screen.