Amazon has Strong Hand Tools Magnetic Corner Squares on sale for $28.24
Shipping is free w/Prime
Create 90 corners by holding from the outside, providing you with an unobstructed area for inside tack welds.
One side corner “relief” provides clearance for tall lips.
Use the outer edges of the Corner Magnet for setting up materials at 60.
Time saving magnetic tools for use in the shop & in the field.
Max. Pull Force: 30 LBS (14 kg)