The ‘twin object’ in this case, is the dark brown object, that represents one of two arms support a suspended/lifted object (shelf).
The brown object in question, has a ‘lap joint’ cut, on it. I’m aware, after copying and pasting the object, I can use the rotate tool. But another challenge in regards to duplicating the brown piece, that there is a bore hole that measures 5/8" deep, facing the direction of where the suspended object. There’s also a circle hole, representing the ‘marking point’ when the arm is lifted to a 40 degree angle.
If one knows how to replicate the 2nd arm, that will be placed at the pink arrow in the following image, without having to redo bore hole or circular marking hole.
Select the components/groups, Move/Copy to the opposite side, while the copies are selected, right click and choose Flip along>Red Direction.
It would make more sense if you were to make components of these parts instead of groups.
By the way, as exciting as it might be to apply the materials right away, it’s best to wait until the model is closer to complete. You need to get in the habit of making the face orientation correct–blue back faces should not be exposed in 3D shapes. Don’t mask the reversed faces with materials.
In the web based version find Styles. Select one without textures applied. Edit the group, right click on the blue face and choose Reverse Faces. If you refrain from applying materials until you are sure all the faces are correctly oriented, you won’t have to change the style to one without textures.
