49 CFR 192.357
Customer meters and regulators: Installation.
(a)Each meter and each regulator must be installed so as to minimize anticipated stresses upon the connecting piping and the meter.#
(b)When close all-thread nipples are used, the wall thickness remaining after the threads are cut must meet the minimum wall thickness requirements of this part.#
(c)Connections made of lead or other easily damaged material may not be used in the installation of meters or regulators.#
(d)Each regulator that might release gas in its operation must be vented to the outside atmosphere.#