How can I tell if the tension pulley and guide you in my Shimano gear?

I took my bike apart to clean and found that one of the pulleys in the arts is called "Guide" other "stress". The tension pulley has a strong bearing in the center so I'm guessing interchangleable its not the guide pulley. Im just not sure where to go. Although I have a good idea. Can you help?

The guide pulley is superior pulley that guides the chain wheel to the next, the tension is lower idler pulley spring that keeps tension on the chain. The upper bearing pulley allows a little from side to side movement of the chain that allows freedom in the center of the cassette sprockets.

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