Modify | Transform | Mirror

This duplication tool creates a mirrored image of selected objects across a line of symmetry, retaining or discarding the original.

The keyboard ALT key is used to retain the original and create a duplicate.

Turn the view to Top, then use the Mirror tool to create a duplicate across the central mirror axis of Part 1, shown below. Hold down the ALT key to create the duplicate, shown below.

Creating a mirrored duplicate. Mirror axis shown by arrow.

The result of the mirrored Fixing should be correctly assembled, shown below from Isometric and Front view.

Fixings correctly assembled