For single rope technique (SRT) ascenders are the devices that grip the rope and allow a caver to climb to the top of a rigged pitch. The earliest ascenders were simple loops of rope tied around the main rope. There are various forms of these friction knots including the Prusik, Bachmann, Klemheist and Autoblock. More recently mechanical ascenders have been developed that are easier to get on and off the rope, and have a more efficient grip and release function. The general categories include Jumar and Gibbs style ascenders. While there are some advantages to the Gibbs style in caving, most cavers today use a version of the Jumar style, which has an open side and a toothed cam for gripping the rope. There are handled and non-handled versions for use with the hand, chest, knee and foot.