Vertex Constraint:
|  | Make a controller that stick to one point of the model. You hereby can use this controller to constrain any object that you want it to stick to the surface of the model. Kind like the famous "Rivet" script. But the beauty is that it won't fly away after smoothing the model. The component it supports are: vertex,edge,face of polygon objects, the cv of nurbs.
How to use: 1.Select vertex/edge/face of a polygon model,or cv of a nurbs model. 2.Click button in maya shelf (If you installed all shelves of MGTools) or the same icon on MG-Constraint tool. 3.A sphere control will be generated. It is a nurbsCurve object. Now you can use it to constrain other objects. The vertex constrainer is stable in translation. But rotation sometime will be uncontrollable. The new UV constraint has been available now ,so use UV constraint is preferable. The number of generated controllers is depend on how many components you have selected. Two vertex means two vertex constraint controller, one face means only one. Tips: Right mouse button clicking on button /"Clear all vertex constraint": Select a vertex constrainer and use this to completely remove this constrainer. It is a handy way to clear that constraint completely.