617 589 01 09 00 Socket

Use/specification:
17 x 20 mm serrated socket, ½” square drive for removing and installing pressure valve holder on M / RSF and ERE injection pump.

Engines 601, 602, 603, 605.91, 606.91 /96, 615, 616, 617.91

http://www.startekinfo.de/etools/
One of the other threads had to above site for Mercedes special tools.