It actually takes two 10mm wrenches. One for the fitting and one for the gauge, the one for the gauge is the counter pressure that keeps you from destroying the gauge (provided it's not the gauge that's bad). If you don't use both you stand a good chance of twisting the innerds out of the gauge.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.