The rating determines the risk category of an instrument. It goes from 1 to 6, where 1 represents the category with less risk and 6 the one with the highest risk. Therefore, equities and indexes on 1 will have the lowest margin requirement (and highest collateral requirement for equities), which increases (and decreases for collateral on equities) at each next rating level. Rating 6 has the worst margin or collateral requirements, set to 100% of the value of the underlying.