Police Batons

There are several variations, but most common are the telescopic or expandable batons and the side-handle batons.
At the end of the 20th century, a popular type of telescopic straight baton or friction lock baton was made of steel tubing which collapsed together for carrying, then slid apart to expand. A small metal knob on the end added weight when the baton was used as a bludgeon. Manufacturers include ASP, Monadnock, Casco and Hiatt.

Side-handle batons, typified by Monadnock PR-24 and made infamous by the LAPD in the Rodney King beating, come in both rigid and expandable models. The rigid models are typically made of polycarbonate. The expandable models usually have an aluminum chassis from which a polycarbonate section extends. Almost all side-handle batons in use are made by Monadnock.
Side handle batons are derived from the tonfa, a Japanese martial arts weapon, and are used with a similar fighting technique.

Both types of batons have their advantages and disadvantages. Side-handle batons are more flexible, enabling many more kinds of strike and block, but they require more training to use than straight batons. Side-handle batons are also very bulky. Expandable straight batons are more compact and are easier to carry covertly and when driving.
Up until the mid- 1990s British police officers carried traditional wooden truncheons of a sort which had changed little from Victorian times, but since the early1990s all forces have chosen to replace truncheons with more modern side-handle and telescopic batons for all but ceremonial duties.

References
http://www.therfcc.org/bludgeon-67475.html