As subject header...

6 brand new metal boxes are countersunk into the blockwork walls in the
kitchen. The block work walls are then plastered using thistle hardwall
base coat and Thistle skim coat.

When doing 2nd fix eletrics it is found that one of the screw hole lugs
on one of the new metal back boxes has no thread so only one screw
instead of two can be used to secure double socket faceplate to the new
back box.

Are there any better solutions than digging out the new metal back box,
fitting new box and redoing plaster around the replacement box?

Regards

Stephen.