Get 15 pages of large, colorful gears that show the interlocking principles of STEAM and the engineering-design-process. Each gear is about 8 inches across, plus the words written across them.
full-page designs include:
STEAM LABS (colored words, grey gears)
Science, Technology, Engineering, Art, Math
Engineering Design Process (colored gears, black words)
Ask, Imagine, Plan, Create, Improve, Communicate
As large as these are, you could certainly do 1 or 2 bulletin boards with them, adding more class-appropriate content with them,