A deck fitting used to secure line or wire rope with two protruding horns is called a __________.

The fitting described as having two protruding horns for securing line or wire rope is known as a cleat. Cleats are commonly used on boats and vessels to hold and secure ropes in place, facilitating safe mooring and docking. The two horns allow for easy tying and untying of lines, making it straightforward for operators to manage the tension and secure the boat effectively.

While other options like bitts and bollards are also fittings used for securing lines, they typically have different designs and uses. Bitts are vertical posts on a ship that are also used for securing lines but do not have the protruding horns characteristic of cleats. Bollards, on the other hand, are substantial posts on a dock or pier where ropes can be secured, usually more robust in design and not necessarily featuring the two-horn structure. The term "notify capstan" is not a standard nautical term, which makes it an incorrect choice as well. Therefore, the context and structure make cleats the appropriate answer for the description given.