Question about "Remove from cart" link

[newsomjk]

In the review cart page, each product has this link:

.../component/virtuemart/cart/delete?cart_virtuemart_product_id=664::666:3;&Itemid=0


I know the 664 is the product id, what are the 666 and 3? I thought the 3 was the Custom Field ID as that's the custom field id for the iStraxx download plugin... however products that don't have that plugin as a custom field still have the 3 so that can't be it.