Samsung Electronics GmbH
Hello,
We are happy to help you. For the Samsung LU28R550UQRXEN monitor, you need a wall mount with a VESA screw hole size of 75.0 x 75.0 mm. For further information on the wall mount, please refer to the operating instructions on page 16, which you can access via the following link:
https://downloadcenter.samsung.com/content...
(Please copy the link into a browser).
Best regards from Schwalbach,
Your Samsung Service Team

The monitor requires a VESA wall mount type 75 x 75 mm. This is somewhat unusual, as many VESA mouts are 100 x 100 mm.