I have created one end of a symmetrical component within Assembly (New Part) and then mirrored it.  However, the two halves are not merged into one component  but they remain as two separate components butted together.  I tried two methods unsuccessfully.

1.  I drew the sketch of the new part on the plane I would use as the mirror plane, then extruded the sketch to the surface of an existing component. I then mirrored both the new and existing components using the mirror plane.  The two halves of the new component were not merged. I deleted the new component. 

2.  I then drew on the surface of the existing part the sketch of the new component and extruded it to the mirror plane.  I mirrored both new and existing components using the mirror plane but the result was the same, butted not merged. .

Is there a way/option to make the two mirrored parts merge into one component or do I have to create in different method?  I searched Help and this forum without success.

I am making all the components within Assembly to allow me to make different sized models by just resizing the "anchor" component to which the sizes of all other components are relative.

Advice please.

Bevin