The first letter of the meter unit identifies the type of threads on the unit. Meter units that begin with the letter “F” denote inch threads.

Threaded into a junction or junction header with a tail tube leading to the bearing. The inlet thread on the “FJ-” meter unit is 5/16-24 to mate with standard junctions and junction headers. The “AJ-” meter unit has the metric-M8xl thread which is very close to a 5/16-24 thread. There are three different “Junction” types identified by the third letters “B”, “C” and “D”. Type “-JB” is the most commonly used meter unit and has a 5/16-24 or M8xl outlet thread for a 5/32 tail tube to the bearing. The type “-JC” also has a 5/16-24 outlet thread but has a tubing connection insert for a 3/32 dia. tail tube. Type “-JD” are thinner than standard junctions and also have closer hole spacing. Type “-JD” are made from 5/16” hexagon bar and have a 1/4-28 outlet thread to accommodate the 5/16 hex compression nut #B3610.