I always got confused about the “Filp on XXX axis” options from the r-click menu; I have given up on them and use the scale tool when I want to flip things - it’s much more intuitive (to me anyway):
With the scale tool, select/drag the middle dot of the plane you want to flip in, type in “-1” and hit [return].
This has the advantage that I can draw a line to represent the mirror plane, use [shift-click] to include it in the selection, copy all this [ctrl+c], use [edit | paste in place]*, then use the scale tool to flip the newly pasted objects; it I don’t need to re-position them.
(^ this is really handy for components like the chair leg above)
The attached example.skp (189.8 KB) has 1 “corner” component, flipped to duplicate it in all 8 directions.
(* note that if you paste a line in place over the top of an existing (identical) line, then it will be removed from the pasted selection - you may need to add it to the selection again before flipping)
[edit] - PS if you want to correct the component’s axis before flipping it with the RGB options, you can either select the component and “change axis” from the r-click menu, or (if you haven’t already made duplicates) explode it, then immediately re-create the component while all the geometry is still selected. - This will set the axis to the global axis and is often quicker.