1/8 oz. cranks usually have # 8 or #10 hooks. #1 split rings.
1/4 0z. usually have #6 or #4 hooks. # 2 split rings
1/2oz. usually have #4 or #2 hooks. # 3 or #4 split rings.
The above is generalizing because differant brands sometimes use differant sizes.
Buy a good pair of split ring pliers .
It's a good idea to buy the Rick Clung split rings (oblong shape ) at BPS ON LINE.
I do use # 2 hooks on 1/2 0z. traps but it is a personal preferance.