A set of 2 pcs large scale magnetic set squares.
Simply pull apart, place inside and outside your 90-degree corner and snap into place.
The snap and glue set squares hold the two pieces of plastic in place and allow you to glue them at the right angle without further worry.
After curing of the adhesive do remove easily the Snap & Glue angle magnets.
Very strong magnets to handle walls up to 7-8 mm thick.