Originally Posted by Aage
I don't know what a "spline" is either, so if you found out, please tell us? But it you didn't, might be the time to ask...
The Spline is the 4" wide piece of 3/4" plywood glued and screwed underneath the seams of the plywood floor. They are item 22 on the diagram Aage posted. I marked them on the drawing for a couple of reasons:
Those frame cross members are 3/4" lower than the other ones to accommodate the splines.
They mark where the seams in the plywood floor are.
I wanted to remember where they were when I was planning out gray tank locations since they are wider than the frame cross members.