jQuery UI’s slider widget have all the features needed for a jQuery range slider: working as a single or range slider, default values and man/maxvalues. However, the smallest download size for it was still ~40kb. Too much for a slider.
Another one is noUiSlider. It have all the things needed and with a size of 2.7kb. There is support for single or double handles, custom starting values, vertical/horizontal orientation and the ability to get /set values.
Also, it works on touch devices and can be customized with CSS completely. Just a perfect widget for any UI.