I think I saw a reference to them being 12" somewhere but, I can't find it. Does that sound reasonable?
an entire foot of dimensional error in our scale is only 2mm and change. Make them whatever size looks good to you.
LOL. That is probably the right answer but, I'm too far gone to accept that. Using a picture that I had taken aboard BB-57 last year and multiple references that state the deck planks are 2" wide on US battleships, I'm estimating that the ones on USS Massachusetts are 12" in diameter and 12" tall. The tops are 14" in diameter and 1/2" thick. Their centers are 32" apart at the base. The base is 48" x 16". Assuming British deck hardware is similar, I'll use these dimensions.
What ever size you print them, they will be fine. Little plastic bits flying in the air is just too entertaining.
I think your bits are a little too bitty. I took some measurements on a picture of the Missouri, came out to 24" tall, 21" diameter which checks better with how big I remember them to be. Deck planks are about 3.5-4" wide. So how do your drive/pump/guns work? I guess it is more fun to shoot detail off a boat that is DIW a couple feet from shore, but if the pump doesn't work it will probably sink too quickly to really get to do damage. And less fun for the captain...
What you've estimated is close to what I found here : http://www.floatingdrydock.com/fittings.htm They list a 1/96 scale 20" Bitt as being the correct part for an Iowa Class BB.
I resized the 3DP part to 20" nominal size. https://rcwarshipcombat.com/resources/20-us-battleship-bitts-in-1-144-scale.83/
