Normally one finds two variations in the original form of the mandolin - the acoustic and the electric (solid block).
The mandolin in its original form is typically an acoustic stringed instrument about 60cm (2 ft) long with deeply vaulted ribs and a table slanted downward at the lower end. It has a neck-cum-peghead attached to a hollow oval shaped sound box. It has four pairs of loop-ended double rib fastened metal strings secured to hooks on the body on one end, and passed across a low bridge (on the sound box) and a nut (on the finger board) to the pegs inserted into a rectangular peg-box. A small flexible plectrum is used to vibrate the strings. A feature of mandolin playing is the constant reiteration of all long pitches, which counteracts its weak sustaining power.
The thinnest string is called 1st string, the next string is the 2nd string which is slightly thicker, and so on until the fourth string.
The acoustic Mandolins are unsuitable for carnatic music. The electrically modified Mandolin is the one used by U. Shrinivas which is suitable for "gamakas" (sustained notes).