Martin 000/OM Customs
Generally, with a few exceptions, 000 and OM have the same body dimensions but have different scale lengths.
The OM body size will have a long scale (25.4 Dreadnought scale), and 000 will have a short scale (24.9” scale).
The main effect associated with scale length is the string tension. The tension of the strings effects the power and feel of a guitar. For short scale, the top will have slightly less tension and the feel of the strings will be a little easier compared to long scale.