If you're referring to the length of the rod, then yes, it's pretty key to get the proper size. A tension rod that's even 1/2 inch too long will "bottom out" and fail to do it's job.
It would be like putting a bass drum rod on a snare. Not gonna work.
If you are wondering if you can cut it short with a hacksaw, don't bother. Get the correct part.
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.
On drumkit drums it's not a big deal, but for high tensions, don't mess around. Get the recommended part.