THRESHOLD EFFECTS IN THREE-BODY KINEMATICS J. Fiol$^\ast$, R. O. Barrachina$^\ast$ and V. D. Rodr\'{\i}guez$^\sharp$ $^\ast$Centro At\'omico Bariloche and Instituto Balseiro, 8400 S. C. de Bariloche, R\'{\i}o Negro, Argentina $^\sharp$Departamento de F\'{\i}sica, Universidad de Buenos Aires, FCEyN, 1428 Buenos Aires, Argentina We show how the single-particles' double differential cross sections (DDCS) in breakup collisions are intertwined by the dynamical constraints. In particular, we study the corresponding relations among threshold and cusp structures and identify some of their general properties by means of a final-state interaction theory. Finally, we show how these structures change with the relative mass ratios of the three particles in the final state.