Thomas carriage with two hook couplings ?

Hi All
One of the carriages in a second-hand collection I bought for my son has hook (not loop) couplings at both ends. As far as I can see, it is designed this way, not a botched repair. I can't find pictures of a similar carriage online, and wonder if anyone can shed some light on it? It is little more olive green than shown in the photos.

On the underside it is stamped:
MADE IN THAILAND
© Britt Allcroft
(Thomas)
Limited 1999

Internally is has part numbers 9R593 P01 and 4R331 P01

Thanks in advance,

Best wishes

Tom

Here are some pictures:




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