How to Select your Oxford Punch Needle size:
First decide if you want Regular or Fine. Regular is a thicker needle allowing you to use thicker yarns (weight 4 or 5). Fine is a thinner needle able to use thinner yarns (weights 1, 2 and 3).
Second decide your loop length. The numbers correspond to loop lengths.
#8 - 1/2" loop length
#9 - 3/8" loop length
#10 - 1/4" loop length
#13 (available only in fine) - 3/16" loop length
#14 (available only in fine) - 1/8" loop length
My favorite tool is the #8 Regular (I like a longer loop length). The #10 Regular is my second fav.