Emerson Rosemount 5408 Reference Manual page 42

Mechanical Installation
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Place a suitable gasket on the tank flange.
Place the customer supplied flange over the gasket.
Tighten the bolts and nuts with sufficient torque for the flange and gasket choice.
Apply anti-seize paste or PTFE tape on threads according to your site procedures.
Gasket may be used as a sealant for adapters with 1½- or 2-in. BSPP (G) threads.
Lower transmitter with antenna and flange into the nozzle.
Reference Manual