Bitt
A Bitt is a set of one or two strong vertical posts fixed to a ship deck, used to secure mooring and towing lines by turning them up in figure-of-eight turns. Double bitts — two posts on a common base — are the usual arrangement for making fast heavy lines.
Bitts differ from a bollard, which is more often a single post on the quay, and from a cleat, which is a smaller horned fitting for lighter lines. Towing bitts aft are built especially strong to take the load of a tow.
Bitts are the fixed strong points a ship relies on to make fast mooring and towing lines. Their strength and the way lines are turned up on them decide whether a line holds safely under load, so they are a basic but critical part of the deck fitting-out.
What is the difference between a bitt and a bollard?
A bitt is usually a pair of vertical posts on the ship for turning up lines; a bollard is more often a single heavy post, especially on the quay. In practice the terms overlap.