How can I get the length of an edge of an object using it's index and snap them together using GN

Question

How can I get the length of an edge of an object using it's index and snap them together using GN.

Example:

My goal is to have:

1. Geometry Nodes generate a smaller box with the same height as another objects edge length, which is acquired from the objects edge index (in the yellow color located at index 4)
2. Have their vertices snap together. See image below.

But I'm having trouble with getting the edge length correct. I tried 2 different ways see image below.

And

Answer 1

This one works by capturing your target solid's edge-vectors, edge-lengths, and edge-normals, before converting its edges to points, and instancing a unit-cube on the points.

the unit cube is offset by .5 in X and Y, before instancing, so one of its vertical edges is on its origin.

The captured attributes are then used to scale and orient the cube.

You can select the target edge in the modifier interface, and adjust the spin of the cube around it:

Answer 2

you can do it with this node setup:

result:

Important node is here the transfer attribute node so that the position is from the group input node (the "original cube").