The thickness of a girdle can affect a diamond’s value and durability. It can range from extremely thick to extremely thick. Diamonds with girdles that are excessively thick or thick normally are less desirable. Yet, girdles must be thick enough to retain the weight of prongs when the diamond is mounted onto a ring, but not be too thick as that would retain much of the diamond's weight, making it look small for its weight. The ideal thickness of a girdle ranges from very thin to slightly thick.
In fancy colour diamonds, a thicker girdle is acceptable as it will help to enhance the colour effect visually. In some fancy shape diamonds such as pear shape, heart or marquise, the girdles can range from thick to very thick in the area of the points and still be considered acceptable. They are there to protect the points from chipping.
Even though diamond is the hardest substance on earth, it also has a weakest point which is referred to as the culet. Culet is the lowest point of a diamond and it is where all facets in the pavilion are drawn in. The most valuable diamond usually does not have a culet. In some antique cut diamonds, culets must be apparent to indicate a certain type of cut, for instance, old mine cuts and European cuts.