On standard round HVAC slip-joint pipe and fittings, the male/crimped end points with the direction of airflow. The female end receives it. Mark airflow before assembling so the run is not built backward.
The male or crimped end points with airflow; the female end receives it.
Ask only when airflow direction is genuinely unclear from the equipment, branch path, drawing, or labels.
Watch out
Do not point the crimp against airflow. Do not crimp both mating ends. Do not force a damaged, collapsed, or uneven crimp into the receiving end.
Check
Where is the air coming from and where is it going?
Which end is male/crimped?
Is the next piece the female receiving end?
Was a cut pipe end field-crimped evenly enough to seat without crushing or splitting?
Will the run still disassemble and reconnect in the planned sequence?
Steps
Confirm the actual airflow direction from the system path or approved drawing.
Identify the male/crimped end and the female receiving end.
Point the male/crimped end with airflow.
Dry-fit the joint before fastening.
Fasten and seal the connection using the approved project or shop method.
Say this to your foreman
I traced airflow from [equipment/source] toward [destination], but this run is not marked. Can you confirm airflow direction before I crimp and assemble it?