This ad features a 3" down tube stem with an 18.8mm joint on the outside MALE portion (the mounting joint in the water pipe) - and a 14mm joint size on the FEMALE portion (where the head piece bowl fits in).
The down stem also has 6 ground slots in the bottom of the stem.
The length of the down tube stem is 3" measured from the bottom of the ground joint to the end of the stem.
The flange at the top of the down stem is 1" in diameter and 3/16" thick.
The over-all length of the stem is 4", measured from the lower edge of the flange to the slotted end of the stem. (see the last picture)
Good quality glass construction.