Been putting this off, but SWMBO is putting the pressure on. I have a
fairly heavy oak framed mirror, which is to go over the fireplace.

I am not sure that nylon cord over 'J' hooks will hold in the long term, and
was thinking of using those flush fixings that screw to the wall & the
mirror and then interlock. Problem is, to ensure that they fit together,
they will only take a No.4 screw. This is fine for the mirror plate, 4x
No.4 1/2" will be fine.

Any suggestions as to what I use to fix the 'wall' plate? It will be fixed
into concrete blocks so rawlplugs will be fine, only issue is that No4
screws are too small!!

Any suggestions as to how I can fix the mirror or the wall side of the flush
fixing? To be clear, anything larger than a No.4 will stop the plates from
locking together.

All ideas gratefully received.

TIA

SalesGuy