A pintle is a pin or bolt, usually inserted into a gudgeon, which is used as part of a pivot or hinge.
Pintle/gudgeon sets have many applications, for example: in sailing to hold the rudder onto the boat; in transportation a pincer-type device clamps through a lunette ring on the tongue of a trailer; in controllable solid rocket motors a plug moves into and out of the motor throat to control thrust.
In transportation, a pintle hitch is a type of tow hitch that uses a tow ring configuration to secure to a hook or a ball combination for the purpose of towing an unpowered vehicle.
As a weapon mount a pintle-mount is used with machine guns as the mounting hardware that mates the machine gun to a vehicle or tripod. Essentially the pintle is a bracket with a cylindrical bottom and a cradle for the gun on top; the cylindrical bottom fits into a hole in the tripod while the cradle holds the gun.
In furniture, a pintle is usually fitted to a caster; the pintle is then inserted into a base, fixing the caster to that base.
In rocketry, a pintle engine uses a single-feed fuel injector rather than the hundreds of smaller holes used in a typical rocket engine. This lowers the cost of engine manufacture while surrendering some performance. Grumman used the pintle-based Rocketdyne RS-18 for the Ascent stage of the Apollo Lunar Module. TRW used this same injector for the Descent Propulsion System on Apollo's Lunar Module. Notable modern uses are on the engines developed by SpaceX.
Pintle is also a common term used in the design of aircraft landing gears. It describes the attachment point between the landing gear structure and the aircraft structure. The pintle is the bolt around which the landing gear rotates when it is extended/retracted into/out of the aircraft. The pintle is a highly stressed component during landing manoeuvres and is often made from exotic metal alloys.