Strong Hand Tools, Angle Magnetic Square Kit, Inside/Outside Magnets, Fixed Angle, 90° (30°, 60°), Mag. Pull Force 20/33 lbs, 3″/5" Length, Welding Square, MLDT350 - - Amazon.com
Flutesan Neodymium Round Magnet with M6 Male Thread, 90 lb or 150 lb Round Magnet with Bolt Stud Mounting Magnet for Lighting, Camera and Other Brackets (4, 90lb Magnet): Amazon.com: Industrial & Scientific
90 Degree Fixed Magnetic Welding Clamps | Eclipse Magnetics