How are flat car deck boards attached

[wcfn100]

And then some of the boards that are place in lengthwise down the center look like they have larger counter-sunk
holes drilled in them with conventional hex-headed bolt heads down in them.

I'm wondering if they are all the large counter sunk holes just the ones on the outside have some sort of cap.  I think the button head ones are not original hardware.

Here's one I shot.







Jason

[Chris333]

But those cars are modern.

[wcfn100]

One drawing for an older car I have references 1/2" carriage bolts.  The drawing appears to have a counter sunk hole, but I can't be 100%.

Jason