What size buttons do I need for a Madcatz TE fight stick?

I’m looking here:
Arcade Sticks Parts Push Buttons - GameShark Store

and i see 24mm and 30mm.

which one should i choose?

or

are 24 mm start and select? and 30 being regular buttons?

30s are the main 8(6 in my case) & 24s are start/select.