Pneumatics connectors, thread, sizes

Hello guys, I need advice and help

I am a maintenance technician at food manufacturing place, my boss requested me to fix air leaks around machinery pointed by the external
energy usage survey.

The problem is I dont have experience with pneumatics installations, most of the leaks are around connectors, fittings etc
there are places where i can stick a lot of ptfe tape and that does the job, but there are places where fittings are corroded and needs
to be changed and here is where my questions raise

how do i recognize type of threads and sizes used

some air lines are in mm, some air pipeworks are inches, some are bsp, any guide? advice? do i measure inside or outside, its
very difficult for me as there are like 50 types of connectors, couplers, reducers and quick fittings used here and there

what about pressure regulators ? some of them have cracked filter bowls, so I cant fix that, I could replace that, but its still the case
of proper size of thread, hose, pipework etc

And I am going to be responsible for ordering parts :(
 
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