Thanks guys. I couldn't find much clear info when I did a search so that's very helpful (and yes ringleheim I do build WW1 aircraft but that link is very helpful too to brush up on skills).

So just to be really clear the wooden beam is sandwiched between 2 long thin pieces of metal with bolts and the ends are also metal?

Cheers for that. Looking at the built Tamiya beam also is there a possibility that the back was metal also? The reason I ask is because Tamiya has made it so it looks like the back is part of the 2 other sides and there's also 2 small parts on the back that stick out. It looks like the top, back and lower sides are all one piece with the wooden bit in the middle.

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Cheers for that. Looking at the built Tamiya beam also is there a possibility that the back was metal also? The reason I ask is because Tamiya has made it so it looks like the back is part of the 2 other sides and there's also 2 small parts on the back that stick out. It looks like the top, back and lower sides are all one piece with the wooden bit in the middle.

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Not sure about that. The beams were a bit wedge shaped or tapered on the short axis according to the Haynes guide for the MK IV. Doesn’t seem like it would be practical to make a “box” on three sides that way. They were made so they wouldn’t “roll” when a track was driven over them, like a wedge, otherwise they’d have a tendency to damage and wear “square” corners under a track. My understanding is they were “chained” or clipped” to the track links via a grouser, and moved around the circumference of the tank to assist in climbing out of a mire or ditch— that’s what those rails on the top of the vehicle are all about. Must have been a muddy, dirty job. But I think they had metal on two sides and wood on two sides.