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A rowlock UK //, sometimes spur (due to the similarity in shape and size), oarlock (US) or gate (AUS) is a brace that attaches an oar to a boat. When a boat is rowed, the rowlock acts as a fulcrum, and, in doing so, the propulsive force that the rower exerts on the water with the oar is transferred to the boat by the thrust force exerted on the rowlock.
On ordinary rowing craft, the rowlocks are attached to the gunwales. In the sport of rowing, the rowlocks are attached to outriggers (often just called "riggers"), which project from the boat and provide greater leverage. In sport rowing, the rowlocks are normally U-shaped and attached to a vertical pin which allows the rowlock to pivot around the pin during the rowing stroke. They additionally have a locking mechanism across the top of the "U" to prevent the oar from unintentionally popping out of the rowlock.
Originally rowlocks were two wooden posts or thole pins that the shaft of the oar nestled between.