 The antiparallelogram has been used as a form of four-bar linkage, in which four rigid beams of fixed length (the four sides of the antiparallelogram) may rotate with respect to each other at joints placed at the four vertices of the antiparallelogram.In this context it is also called a "butterfly" or "bow-tie linkage".As a linkage, it has a point of instability in which it can be converted into a parallelogram and vice versa.