An improved apparatus for forming curved structures comprises a plurality of pivotally connected sections, each section having a track portion, and a strap member adapted for slidably engaging the track portion of the sections such that the sections are movable to form a radius of curvature. The sections of the apparatus of the current invention are initially pivotal in relation to one another. Following position in a desired configuration, one embodiment of the current invention provides a tab or protrusion carried by one section which is compressed against the base portion of an adjacent section to prelude further pivotal movement. In another embodiment, the pivotal connection between adjacent sections is further compressed, crimped or swaged to preclude further pivotal movement.