Old School Low Tech Approach:
Not having a caliper, you can use a
white thread and a Sharpie Fine Point
pen. Put a mark on the sway bar. Wrap
the thread around the bar and mark it
for length. Measure the thread, mark-
to-mark. Now you know how big around
the bar is. Doing the math, you will
find the approximate diameter of the
sway bar. Most bars are common/whole
numbers like 1 1/2" or 1 3/4", this'll
get you into the ballpark.
BTW--your E450 Chassis has HUGE sway bars
as OEM stock...