English to Italian Tech/Engineering Mechanics / Mech Engineering coolers

If the double tube cooler is fitted with a leakage detector, the size G 1/4" upper air venting nipple must be removed to prevent exposing the detector system to an excessive pressure.
The leakage detector should be fitted to the lowest nipple.
We recommend tightening the header bolts before commissioning the cooler.
Torque of bolts and the order in which they are to be tightened, see Figure 3.

I need some help with the Italian translation of header bolts.
I'm not sure whether the correct translation for "header" is "collettore" but would that help?
I would appreciate your help.