A hydrant wrench is a tool used to remove fire hydrant

Fire hydrant

A fire hydrant , is an active fire protection measure, and a source of water provided in most urban, suburban and rural areas with municipal water service to enable firefighters to tap into the municipal water...

 caps and open the valve of the hydrant. They are usually adjustable so as to fit different sized hydrant nuts.

In France

In France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

, the hose and hydrants are linked with Guillemin symmetrical clutch (raccord symétrique Guillemin), which requires the rotation of 1/4 turn of a ring to be fastened. The ring is notched.

The wrench is called "Guillemin wrench" , but the firefighters call it "tricoise wrench" (clef tricoise, [kle tʁikwaz]). The curved part applies on the ring, and the hooked part clutches a notch.

Big tricoise wrenches are placed in fire trucks

Fire apparatus

A fire apparatus, fire engine, fire truck, or fire appliance is a vehicle designed to assist in fighting fires by transporting firefighters to the scene and providing them with access to the fire, along with water or other equipment...

, and are mainly used to fasten the big hoses, e.g. ∅110 mm hoses to feed the pumper tank from the hydrant (∅100 mm for the clutch). Small tricoise are made of brass

Brass

Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 and hang at the fire belts; they are used to fasten the small hoses, e.g. ∅70mm to ∅22mm hoses (∅65mm to ∅20mm clutches).

The shape is sometimes adapted so it can be used as a tool for other purposes; it is then called "polycoise wrench" or "Deschamps wrench". These tools are used to

• 12mm female triangle wrench: opening the gas
  Gas
  Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
  
   and electricity
  Electricity
  Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
  
   standard boxes of EDF
  Électricité de France
  Électricité de France S.A. is the second largest French utility company. Headquartered in Paris, France, with €65.2 billion in revenues in 2010, EDF operates a diverse portfolio of 120,000+ megawatts of generation capacity in Europe, Latin America, Asia, the Middle East and Africa.EDF is one of...
  
  -GDF
  Gaz de France
  Gaz de France was a French company which produced, transported and sold natural gas around the world, especially in France, its main market. The company was also particularly active in Belgium, the United Kingdom, Germany, and other European countries. Through its part-owned Belgian subsidiary SPE...
  
  
• 15.6mm female triangle: opening the boxes of the fire hydrants;
• 5×5mm to 8×8mm square female wrenches: opening the doors without knob, the ventilation accesses and the closets containing firefighting equipment in some public locations;
• 12.5×12.5mm square female wrench: open the dry riser
  Dry riser
  A dry riser is a main vertical pipe intended to distribute water to multiple levels of a building or structure as a component of the fire suppression systems. The pipe is maintained empty of water. The dry riser is the opposite of a "wet riser" or "wet standpipe" system where the pipes are kept...
  
  s;
• screwdriver
  Screwdriver
  A screwdriver is a tool for driving screws and often rotating other machine elements with the mating drive system. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver...
  
  : opening the bathroom and toilet doors;
• unfastening nuts
  Nut (hardware)
  A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...
  
   with the 13, 17 and 19mm six-point wrenches.

In the United States

The shape of a hydrant wrench is sometimes adapted so it can be used as a tool for other purposes such as:

• Storz and spanner hose couplings
• Rocker lug couplings
• Water meter
  Water meter
  A water meter is a device used to measure the volume of water usage. This article provides an overview of technical aspects of water meters. The worldwide prevalence of metering as well as its economic benefits and costs are covered in the separate article on water metering.In many developed...
  
  shutoff valves
• Gas cock valves
• Pentagonal nuts
• Square nuts.