I'm writing a thank you letter for a professor whose lab I am working in and I play a fairly small role. Although I have a very tiny part, for me the lab is a huge part of my life.
Is there an English saying that describes a small part of the whole? Like a tiny screw in the machine or a walk-on in a play? I was going to go something like "a small keg in the brewery" but I don't know if that makes much sense.
Thanks so much!