Set how many letters fit around the rod, and your text is scrambled exactly as if wound around it — written along the length at each position, then read off around the circumference. The grid below shows the actual wrap.
The Rod, Unwound — Visual Grid
How this works — text is written into a grid with one row per full wrap around the rod, filling left to right. The scrambled message is what you'd read going down the strip's length at each position around the rod — column by column. Both sender and recipient need a rod of the same circumference.