A diminished seventh chord (dim7) has a diminished triad plus a diminished seventh interval. For instance, a Cdim7 chord has the notes C, Eb, Gb, A.

 

The Swars are Sa, ga, Ma and Dha.

 

As the interval between each pair of notes is a minor third, the chord sounds the same regardless of the root. Edim7 sounds the same as Gdim7, Bbdim7 and Dbdim7. 

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Let me also try to clarify interval naming conventions. The same interval can have different names! The interval from C to B (just before the octave) is called a major 7th interval (Sa to Shuddh Ni). The interval from C to Bb (Sa to Komal ni) is called a minor 7th interval. And the interval from C to A (Sa to Shuddh Dha) can be called either a diminished 7th interval or a major 6th interval. So, if you are playing a C6 chord (C, E, G, A), the A note here is referred to as a major 6th interval. But if you are playing a C dim7 chord (C, Eb, Gb, A), you would refer to the A note as a diminished 7th interval! 

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A dim 7 chord can sound very unsettling. It does not have a Perfect 5th interval or Pa note. Instead, it has a Teevra Ma, and the interval from Sa to Teevra Ma does not sound satisfying and is known as a dissonant interval.

 

Diminished chords work well as passing chords. So, if you are playing in the C Scale, and the melody moves F to F# to G, you can move from an F (F, A, C) to a F# dim (F#, A, C) to a chord (C, E, G). This will sound nicer if you play the appropriate inversions and let the lowest or highest note move from F to F# to G!