A countersunk nib bolt is a type of bolt that has a countersunk head and a nib or projection on the underside of the head. The nib is designed to engage with a slot or hole in the mating component, providing additional security and preventing the bolt from rotating. Countersunk nib bolts are often used in applications where a flush or nearly flush finish is desired and where rotational stability is important. They are commonly found in machinery, furniture, and other applications where a secure and reliable connection is needed.