Number of joints
to constrain

select the number of joints to constrain from the drop-down menu.

Joint1

select the first joint constrained by the coupler.

Joint2

select the second joint constrained by the coupler.

Joint3

select the third joint constrained by the coupler.

Symmetric
properties

allows you to turn symmetry on or off.  When symmetry is turned off, both sides can be edited separately.  When you turn on symmetry, you are prompted to select a parent side.

User-defined
properties

checking this box will automatically change the Properties tab into the User-Defined tab, which will allow you to define the properties utilizing a user subroutine.