Is it 21mm?
I think most are 19mm, but almost all can use silicone instead. Seems the YYF Large Pad Slim 19mm, CBC and K-Pads are also suitable as well.
Correct.
What type of C3 do you have?
If you look at C3yoyodesign – YoYoExpert it will give you a list of C3 yoyos.
If you click each yoyo, then go down the page to the left, there are specs. It will show the size of the pads there.
I mean responses for di base
It says its bigger than19mm
Just use flowable silicone. Problem solved. Hopefully you can get that easily where you live. Here, we often get it at auto parts stores and other large merchants that carry automotive stuff.