Import / Export dry box containers meeting ISO standards can be found in both 8 foot 6 inch ( standard ) and 9 foot 6 inch ( Hi-cube ) heights. Twenty foot boxes are standards only, whereas 40 foot reefers have gone Hi-cube. All 45' ISO dry box containers I have seen are also hi-cube. I haven't seen any 48 foot ISO containers in quite some time; APL was really the only Steamship Co. ( SSCO ) to have them for International service. Most SSCO's also have 8 foot 6 inch height collapsable bulkhead flats; Hapag-Lloyd has a few hi-cube flat racks and steel hinged-top dry box containers as well. Note that all ISO containers are 96 inches wide.
Now we have the goofy stuff: the Alaska SSCO's and Matson. Here in Seattle we have the sister companies Alaska Marine Lines ( AML ) and Lynden Transport (LTI). AML has 20 foot, 48 foot, and 53 foot hi-cube dry boxes, some with a 102 inch width. Lynden has some 53 foot hi-cube reefers !!! Earlier this year Lynden bought Northland Services, who also has all the above sizes of containers. AML & Northland also have flat racks without bulkheads, including a few 24 footers. These odd-ball sized containers stay captive to Northland & AML / LTI barge fleets, so interchange issues don't exist. Note that the 102 inch wide containers have the ISO bottom pockets at the 96 inch width, so they fit on standard chassis'.
Matson Lines, which offers service to Hawaii and the Pacific Islands, has a fairly normal ISO-spec fleet except for their 24 foot dry box containers and bulkhead flat racks. Also some 45 foot bulkhead flat racks. The 24 footers require a different chassis with a gooseneck on the front end; this in turn requires a tunnel on the forward underside of the container. ( All ISO containers over 20 foot in length have a tunnel under the front end so as to snuggle down on the chassis over the drive tires of a truck tractor. This is critical for hi-cubes to remain under 14 foot overall height. ) Matson also has some 20 foot, 24 foot, and 40 foot dry box containers with roof hatches !!! As with the Alaska SSCO's, Matson has their own ships and a captive fleet of equipment, though they do lease containers and chassis from 3rd party suppliers as their service levels dictate.
I don't haul domestic intermodal containers, but my observations are that most of this equipment consists of 48 foot and 53 foot -- 102 inch wide -- hi-cube dry boxes. CR England also has 53 foot hi-cube reefers, maybe Americold does too. These containers are NOT built to the more durable ISO standards, nor will they fit on an ISO container chassis. This is by design, as the domestic carriers Schneider and J.B. Hunt designed their chassis and containers to accept bottom " dog " pockets at the 102 inch width only. I've also been told that one of the carriers ( Hunt ??? ) has a wider chassis gooseneck, and container tunnel as well, just to insure their chassis don't end up hijacked into Port Container service !!!