Say that you have a progression that utilizes two chords (one after the other) a M2 distance apart in the root:
As you can see by the example above, the Eb major triad and the F major triad fit that definition.
What you can do for some added harmonic progression color is insert a diminished passing chord in-between.
Simply, you build a diminished triad on the root of the pitch that falls chromatically in between the two chords:
From there, you would then orchestrate the chords for better voice leading, but the added diminished passing chord gives a little more emphasis to the arrival of the F major triad in the progression.
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