Moving angled lines on Y axis while keeping them in the same place on the X axis

[Anonymous]

Basically I'm trying to create a structural connection face-based family to support a special kind of beam. This support has to fit the beam exactly, so that's why the internal faces are angled (see image bellow).

The only flexible dimension I need for it is the Height, so I created 2 Reference Planes: 1 for the top of the object and 1 for the bottom of the internal part, where the beam sits (the bottom of the object is on the reference level). However, no matter what I try, I can't flex it and have it keep the same internal shape. The internal angled faces "slide" on their angle lines.

I've read all over this forum and my guess is that using Reference Lines instead of Reference Planes will be the solution, but, even after I tryed, I couldn't make it work. The closest problem I found to mine was shown in this post (https://forums.autodesk.com/t5/revit-architecture-forum/locking-a-diagonal-line-endpoints-to-referen...) , however, due to my Revit version being the 2018 one, I couldn't download the anexed file to see how to properly  use Reference Lines.

If someone could help me, I would be grateful.

[Anonymous · Accepted solution]

Use reference lines for this and lock the dimensions for the reference lines.  I attach a family that flexes as you demonstrate for you to deconstruct.

[Anonymous]

Thank you!