Originally Posted by DOT Title 49 - Transportation, page 597
(2) For cylinders manufactured before October 1, 2007, a cylinder
must have its valves protected by one of the following methods:
(i) By equipping the cylinder with securely attached metal caps of
sufficient strength to protect valves from damage during transportation;
(ii) By boxing or crating the cylinders so as to protect valves from
damage during transportation;
(iii) By constructing the cylinder so that the valve is recessed
into the cylinder or otherwise protected to the extent that it will not
be subjected to a blow when the container is dropped onto a flat
surface; or
(iv) By loading the cylinders in an upright position and securely
bracing the cylinders in rail cars or motor vehicles