Montana Title 70. Property § 70-4-103. Rules for determination of principal part

(1) That part is considered to be the principal to which the other has been united only for the use, ornament, or completion of the principal part unless the other is the more valuable and has been united without the knowledge of its owner, who may, in that case, require it to be separated and returned to the owner although some injury results to the thing to which it has been united.

(2) If neither part can be considered the principal within the rule prescribed by subsection (1), the more valuable or, if the values are nearly equal, the most considerable in bulk is to be considered the principal part.