OnMouseDown without collider?

Hello friends! I'm trying to select my shooting tower by OnMouseDown function. It works fine. But I have a sphere collider of that tower much more than itself because I am using a OnTriggerEnter function to detect whether enemies have entered my circle to start fire. So OnMouseDown function doesn't work the way I want.

Is there any way to solve that? Or is there any function that I can use to select my tower without using a Collider?

Thanks in advance!