The larger one is a lock nut.....if you look closely you may see some little holes drilled in it....for seal wire....it also could just have a dot of bright paint so that a Bosch Rep will know if someone has been fooling with that adjustment.....

I don't remember if the Benz pumps have the seal there or not...but I do remember sealing the Dodge/Cummins pumps there.....

SB

Note: I worked as a Bosch Tech for about 6 or 8 months shortly after I retired....left there to go back out to Diego Garcia at the request of the folks that I retired from.....made me an offer that could not be refused....

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG