User-defined constraints in Catia V5 analysis

[sb009441]

Good day,

My question is regarding the definition of user-defined constraints in the context of a Catia V5 FEM analysis. The dialog box for user-defined constraints asks you to define start-middle-end. What do start and end exactly represent? (I have read the help files on this but am still a little confused...) What I am trying to do is define a user-defined constraint between the bores of two conincident holes (in a plate assembly...one hole on each plate) to model a rivet. I am applying my user-defined constraint on an assembly link that I created between the surfaces of both holes. In this case, what does start and end represent? What option should I specify for start-middle-end to reprensent the rivet attaching the two plates?

Thanks in advance for you help,

Simon