Rings that are thinner and more flush to the thumb are the best. The joint is the widest part, so it must be taken into account when measuring. Once you get the ring on the joint, it'll be safe.
If you look at your hand, you will see and feel that the index finger tends to have more flesh at its base. This means that any ring you order will fit quite well. We often suggest that you increase the size of your ring by +1, which will allow you to fold your finger.
Middle and ring finger
Beware of finger joints, especially if the finger is narrow at the base. When choosing rings for these fingers, remember that if it slides comfortably on the joint, it will be much too large for the base and will more than likely swing around the finger.
These fingers need extra attention because people tend to lose their rings all the time - especially when their hands are cold or wet, or when they enter and exit their pockets. The rule is to wear it as tight as possible while being able to bend your finger - if it is too tight, it is better to loosen it than to lose it.
The main reason your fingers expand and shrink is that your body reacts to changes in temperature in your environment. When you are in a cold environment, your body tries to keep your heart warm by tightening your blood vessels and reducing the blood flow to your skin. This process is called vasoconstriction. This is necessary because heat is lost from your skin to the environment, so your body tries to reduce the flow of blood to your extremities, especially to your fingers and toes. This shrinks your fingers and toes, so if you wear a ring on your finger, it will come off.
The opposite happens when it is hot outside. Your body tries to cool itself by dissipating heat through your skin, in a process we all know too well: sweating. As the outside temperature increases, your blood vessels dilate, so your blood flow increases and excess heat in your body can be released into the environment through your skin. This is called vasodilation. This dilation causes your fingers and toes to expand, so if you wear a ring, it will suddenly become much tighter.