It's been so long since I took the Mechanisms class..... I can't remember which connection to use. I have a lever with a spherical pocket in it. Into this pocket is a pin with a fully rounded tip, much smaller than the pocket's sphere. I can't make a ball connection and can't seem to figure out how to use the tangent of it (which is what it really is) as the translation constraint. To put it another way, imagine trying to construct a joint in which a ball rides within a spherical socket whose radius is 3 times the radius of the ball. The pin is constrained in one axis, but the socket moves in an arc.