Student or Learner
1. I will always try my best to keep the size of thread small.
Does this sentence make any sense? If it doesn't, please write the correct one.
I think it's a poor sentence, and requires an article before the last noun.
What sort of thread is being kept small?
"Small" refers to size anyway so there's no need to specify size. You could just say "I will always try my best to keep the thread small". However, if you're talking about threads on forums (like this one), we use "long" and "short", not "big" and "small". If you're trying to assure us that you won't allow your threads here to become unnecessarily long, as so many do, you would say "I will try my best to keep my threads short".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.