Struggling with Required Attributes

[NotHollister.com]

I have an online clothing store that requires products options such as color and size. However, whenever i try to make the attributes required, people can still order things without selecting a size for a radio button. If you have any help or comments, it'd be greatly appreciated. My website is located at www.nothollister.com

[kobra]

https://www.zen-cart.com/tutorials/index.php?article=57

See step #4 and
Default Attribute (Should be used especially on Radio buttons, or if you have an attribute you prefer the customer selects.)