In drafting language the alphabet of lines refers to the "code" names of the different types of lines and how they are used. Dash lines are called "hidden" lines? These are used to show lines for what you cannot see? Say what? This kind of thing appealed to me in high school and I took a keen interest in "cracking" this code. There are center lines, section lines, dimension lines, leader and extension lines to name a few more. I have taken to using colors for the different lines as a help keep me on track when I am reading my "blueprints". At the risk of dating myself, remember the great smell of those dito-master copies your teachers handed out? In the early days, copies of original drawings were made by a process that used special paper, light and ammonia (a foul smelling harsh chemical). In the development process the paper turned dark blue and the lines forming the drawing remained white! Thus the name "blue" prints and it stuck for a long time.
The "button" we are talking about can be seen in the picture to the right. A hole has been drilled through the floor joist. A threaded rod passes between the inner and outer bottom chords of the lattice truss. The button at the very bottom is drawn up tight by the nut and secures the floor joist to the bridge truss. The same system will be used to attach the roof truss assemblies the the top of the bridge trusses.
Puzzler - What next?
Tech Vocab - Camber, Chord, Kerf to the line