Abstract: The present invention is a tool for spacing frame members having an elongated body which has a first and a second track. A cradle, formed by a first head and a second head, can be adjusted to accommodate a first frame member of width W, and a shoulder, formed by a third head, can be spaced apart from the cradle to engage a second frame member, separated from the first frame member by a spacing interval I. Each of the heads slidably engage the first track and the second track of the elongated body, and each have an indexing face which is substantially normal to the elongated body. The heads are lockable with respect to the first and second tracks. Preferably, the elongated body has a bubble level to aid in identifying when the body is horizontal. When a bubble level is employed, each head has a levelling surface, the levelling surfaces being co-planar, providing a discontinuous reference surface for levelling.