There are 3 different series:
- Series LL:
for compressed air, hydraulic return lines, propane, oil heating, automotive engineering, small refrigerating plants, apparatus construction, plastic lines etc.
- Series L:
like series LL but for greater mechanical stresses, compressed air lines etc.
- Series S:
heavy mechanical engineering, shipbuilding, mining, chemical industry, large refrigerating plants, pressure lines etc.
Determining the thread type of metric connections:
d2 = Outer thread diameter
d1 = union nut internal thread diameter
NW = nominal width
SW = key width