The tonfa originated in Okinawa as a millstone handles. Like the nunchaku, they were improvised weapons called into use after rulers and invaders confiscated all metal weapons. The tonfa's circular movements as a farm implement evolved into its rotating strikes as a weapon. The sides of the tonfa are used for blocking and striking, and the ends are used for thrusts, and strikes. By spinning the tonfa around the short handle, tremendous striking force may be generated.  By using the long portion in conjunction with the short handle, the tonfa may be used for numerous come-a-longs and arm locks. 

Because they are so versatile and are not viewed by the public as excessive force, many law enforcement agencies use a version of the tonfa called the PR-24, previously called a Prosecutor, made by Monadnock (shown below). The Prosecutor name was dropped due to its negative connotations. It is interesting to note that Monadnock states that the PR-24 is a uniquely designed weapon that is in no way related to the tonfa. When used for law enforcement, on one is used rather than the traditional pair.

Because of its size, the tonfa is not effective as a present day self-defense weapon.

Reference

• Starrett, R. R. (1976). The Monadnock PR-24 "Prosecutor."  Monadnock Lifetime Products Inc.