I did a little research today on chain sizes available in HO scale for use as flat car load tiedowns and found that there seems to not be a great range of choice. The only 2 that appeared reasonably available were 27links/inch and 40links/inch.
I had previously bought some 40link black chain made by A-Line (Proto Power West). I had also been buying MTH's 60' wood deck flat cars which come supplied with 15" of chain and 8 load adjusters in little plastic bags.
I thought the 40 looked a little light when placed against the Caterpillar stuff I'm using it for mainly although it will probably be OK on the smaller equipment, so I thought I'd check out the MTH stuff.
I had also got, when I bought the A-Line chain a good number of Lonestar Models plastic load adjusters and on placing one of them against the 40 link I could see the links (about 1/2" moulded onto the end of the adjuster) were slightly larger.
So I opened up the MTH bag and could see immediately that it was a larger link chain and was a very close match to the Lonestar. I went about counting the links and after checking 3 times (twice at 32, once at 33), I figured 32 was what it was.
Here's a few pics. The top chain and adjusters are the MTH. The lower the A-Line 40 link and the lonestar adjusters below that.
Then I've draped the chains over the blade of a D9T, 40L on the right, 32L on the left
Next pic shows them likewise draped over the body of the D9T (very unprototypically I admit)
This shows one of the Lonestar adjusters with it's moulded on chain leaning on the blade to show that in a lot of instances this may be all that's needed.
Lastly an adjuster leaning against what looks like it's a lug on the side of the radiator housing of the tractor. It may be that a lot of loose chain is not required and these would suffice in most applications
They are supposed to be available in brown as well as grey, unfortunately not in stock at the time I bought mine.
Footnote: I tried to find a supplier of 32 link chain without success, found a couple of references to it on google but no actual manufacturer or stock listings.
Footnote to the footnote: Here is a pic of a D10T loaded onto a 60' flat, note the chains over the tracks straight down the sides.
The 60' car's decks are 12" wider than the 89'4" ITTX which are also used as machinery carriers, so my D9T's, while most usually appear on 60's would be quite at home on the longer cars and within load limits. To round this off here is a pic of the deck of a ITTX. Note the heavy timbers and the channels for the tiedowns that have been added to what would have been a flush deck car.