F31

F31 or F.31 may refer to:

Vehicles

 * Aircraft
 * Farman F.31, a French prototype fighter aircraft


 * Automobiles
 * BMW 3 Series (F31), a German estate car
 * Nissan Leopard F31, a Japanese sedan


 * Ships and boats
 * F-31 Sport Cruiser a trimaran sailboat
 * HMS Cyclops (F31), a submarine depot ship of the Royal Navy
 * HMS Mohawk (F31), a Tribal-class destroyer of the Royal Navy
 * INS Brahmaputra (F31), two frigates of the Indian Navy

Other uses

 * F31 (classification), a disability sport classification for seated throwing events
 * Bipolar affective disorder
 * Fluorine-31 (31F), an isotope of fluorine