Bluegrass music most often uses the 1, 4 & 5 Major chords, with sometimes an added 2 or bluesy 7. Perhaps the most common chord sequence is 1-4-5 or 1-4-1-5. Songs with minor chords typically use the 6m or 2m, e.g. 1-6m-4-5 or 1-2m-5-1.