How to join these slotted parts?

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Sorry if this is a basic question, but I'm new to fusion 360 and I'm not sure what is the best method for doing this.

I've created 2 parts that should slot together.

As you can see, the top part should just slide down into the slot on the bottom part when assembled. 

What is the best way of joining these 2 pieces in Fusion 360?

I've tried several things, but I never get the joint that I want with the pieces lined up the way I expect.

Thanks.

[fulcrumusa]

Turn the two parts to components and then join them with a Rigid joint using the top surface of the cutout on the upper part and the bottom surface of the cutout on the lower part.

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I tried that but it somehow turned the top part so that it was aligned with the bottom part, rather than at 90 degrees, like I expected.

Is there a way of specifying the angle of the joint?

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I just tried it again.  This is what it looks like after I pick the two centerpoints of the bottom of the slot and the top of the other slot.

It aligns the pieces with each other.   I have the option to rotate one of the pieces, but only on one axes, and it's not the one I want.  

Maybe I'm not picking the points correctly!?

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After playing with it for a while, I realized that if I hover over a face, I can see "control points" appear, and then I can select the approriate control point for the joint.   After carefully selecting my points on the face, I was able to align the pieces the way I want.

Thanks for your help.