Regarding the above post, Pearl rods do tend to look a bit wider. The thread pattern is the same, but the Pearls are a tad more robust and have a tighter tolerance.
It's not just Pearl and it's not just that they
look wider. With the advent of Kevlar heads, tension rods were shearing under the tension. Pearl, Yamaha, and other companies started using wider tension rods on their marching snare drums. (You'll find 'em on tenors nowadays, too.)
If you look at Yamaha's tension rods, the thicker 6 mm version has a dimple on the top of the square head so you can visually tell a high-tension marching drum tension rod from the typical skinnier rods.