TD4 egr

what fits onto the thin tube and ..

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the vacuum hose
i.e. it blocks it ..
( i used a bolt to block the hose )
or could be drilled out for a turbo pressure gauge .. at a guess

what does the T knob do

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is that what others refer to as the 'mushroom' ?
if so .. it be for connecting to the exhaust pipe section with the original clip thing
i.e. blocks the exhaust feed off