I started hauling grain in the 60's and in those days the used bob tails for field trucks. They either dumped into the pit at the elevator or were raised with a hoist. It took over an hour to load 1000 bu of grain, so I saw the floor of a lot of truck floors. A few floors had strips, but most had self tapping screws. I don't think torx came out until the 70's. The ones we used were Phillips. In those days, we used a bit and brace to screw them in. I always found me a big ole boy to push down on the brace to keep pressure on the Phillips head. I prefer 5/16" over 1/4" because I have seen a few 1/4" break during installation. They are so hard, its almost impossible to drill them out and you usually wind up with the hole being too big and then you have a hole in the floor. Once installed, the extra strength isn't needed. In order to remove an old floor, I go to a hole in the wood to start. There is usually a hole or you wouldn't be reflooring it in the first place. I then use an old fashioned grubbing hole and chop between the wood and the crossmember and it will cut the old bolts right off flush with the cross member. Another reason I use 5/16" is that if I happen to hit an old bolt when I drill, there will still be enough there for the threads. The remains of the old bolts are usually soft enough to drill. I don't think carriage bolts through the wood were ever factory. I think that was a country boy fix. I'm not sure if carriage bolts at the end of the boards was factory or if someone put them there during reflooring to give the boards more protection against warping. The use of strips or countersunk bolts was then and is still so that things can be slid across the floor. I use an Isuzu bobtail to transport bottled water on pallets from Costco to my place. The Isuzu is too low for dock height, so they push the pallets in, and when I get to my place, I chain them to the rear and then fork lift them off.
