From what I can gather there were some wagons that had double pegs on all intermediate fixings that would accept 6 ten footers, but these are very hard to come by, its more normal for the 20,30,40 to be doubles, especially today, having said that some wagons have so many fixings its almost impossible to work out what they can carry, 20,30,40, 45, 48' or what ever combo you can fit in, many are not fixed pegs but can slide, thus saving on the number of actual pegs required, ie one peg can be slid into many locations. Of the images I've found its usually 10+30+20, or 10+40+0.
It appears that all Freightliner boxes were fitted with ISO twistlock pockets, as well as side fixings for chain and tackle, the above box has both, photos later when I get home.
Some early corner pockets seem to be fully enclosed, ie only bottom or top opening, but as equipment has advanced then side and end holes were required, many reach stackers actually use the side holes, especially empties where two can be lifted at once, in which case both the side and end holes are clamped with a complex hydraulic fixing.
It also gets more complex when you add in Sealand boxes and their hybrid lock system that only uses two rear locks and a center front internal pocket, though (to my knowledge) no wagons in Europe were ever outfitted with that system which remained a US based system, unlike broad gauge the Sealand fixing took a very long time to die out, and until the Maersk buy out a few years ago all new Sealand boxes & trailers were still built to that system, there's an awful lot of them to be phased out, not just boxes but rail wagons, road trailers and whole fleets of dock trailers on dedicated Sealand terminals. Luckily Sealand had some forsense and added front twistlock pockets as well....just in case the rest of the world refused to adopt their system...which we did
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Hope that helps
