To unscrew a screw with a square-shaped hole, you will need a tool called a square-head screwdriver or a square-drive bit. Here are a few options you can consider:
Robertson screwdriver: This type of screwdriver has a square-shaped tip that fits into a square hole screw. It is commonly used in certain regions like Canada and is available in various sizes.
Square-drive bit and ratchet: If you have a ratchet set or a screwdriver with interchangeable bits, you can look for a square-drive bit that matches the size of the square hole. Square-drive bits are available in various sizes and can be used with a ratchet or screwdriver handle.
Impact driver: If the screw is difficult to remove or if there is limited space, you can use an impact driver with a square-drive bit. An impact driver delivers a high rotational force and can be helpful in loosening stubborn screws.
Make sure to measure the size of the square hole before purchasing the appropriate square-drive bit or screwdriver. It's also a good idea to secure the sink or the area around it to prevent any accidental damage while working in a tight space.