Screw Plug.
Hydraulic Control Plug on the Unimog 406/416.
Buy p/n 1309970032.
Part # 1301800056
Part # 000906030003
Diagram # 011
Part # 0001310856
Part # 0001840556
Part # 8369970030
Diagram # 266
Part # 0019975430
Part # 007604018109
Diagram # 008, 177, 180
Part # 4609971181
Part # 7161690251