Answer:
I go around in circles, but always straight ahead, never complain, no matter where I am led.
I am bought by the yard but worn by the foot
I have wheels and flies yet I am not an aircraft.
My second is performed by my first. A thief by the marks of my whole might be caught. What am I?
I can be short and sometimes hot. When displayed I'm never cold. What am I?
No matter how little or how much you use me, you change me every month.