This is an IKEA SKADIS support for the smaller screwdrivers from the Stanley Set (STANLEY STHT0-62143) you can buy here: https://www.amazon.co.uk/dp/B00K5N2910

In order to fixate it to the IKEA SKADIS board, you need to print 2 of these Improved Universal Low Profile Hooks: https://makerworld.com/en/models/450177