When two people have the same Enneagram type it means there's a fundamental influence upon their personality that is similar, but there are also differences that can't be accounted for by just looking at the basic type. These differences are often explained using concepts such as wings, centers, and instincts.
While the first step to exploring the types is to determine which of the nine types is the best fit for you, once you've understood what that means you may want to then explore the subtleties defined through the many variations of type. Looking at these variations can also sometimes help you find your basic type.
Also called core type, primary type, or dominant type, your basic type is found by identifying which of the nine Enneagram types best describes you. This is what people call "your Enneagram type." Although you can use one of the many names to refer to your type (e.g., type 1 is sometimes called the perfectionist or reformer), it's much more common to use the number since it's not dependent on any one interpretation of the types.
One difficulty with settling on a single type is that you actually are all nine types, just not to same the degree. It can sometimes help when people are having trouble discerning the differences between the types to look at the subtleties described by the type variations.
The types on either side of your basic type type as seen on the Enneagram symbol are said to have an additional influence on your personality (e.g., the wings for type 1 are 9 and 2). One of these two types often has more of an influence than the other and is called your preferred wing (e.g., 1 with a 9 wing or 1 with a 2 wing - commonly written as 1w9 and 1w2).
While you are still your basic type, your preferred wing adds an additional influence to your type to create a variation of your basic type. Two people may have the same basic type yet different preferred wings. Basic type creates similarities while different preferred wings create differences.
When you add wings to the types you go from 9 types to 18 variations of type.
The concept of centers describes three centers of intelligence often called the gut/body center, the heart center, and the head center. Each type is grouped into a center based on its location on the Enneagram symbol: 891 are in the gut/body center, 234 are in the heart center, and 567 are in the head center.
The tri-center approach, also commonly referred to as trifix or tritype, looks at a person as three types, one type from each center. With tri-center your basic type is your primary type and primary center. You then determine which type is dominant in each of the two remaining centers. From those two types you also determine which is your secondary type/center and your tertiary type/center.
For example, let's say your basic type is 1, your dominant heart type is 3, and dominant head type is 5. In addition you prefer type 5 over 3. Your tri-center would then be 1-5-3 where your primary type is 1 in the gut/body center, your secondary type is 5 in the head center, and your tertiary type is 3 in the heart center.
If two people had the same basic type then they would be similar in that way. However, if their tri-centers were different then they would be different based on the difference in the secondary and tertiary type influences.
There are 18 different tri-centers for each type which produces 162 type variations for all nine Enneagram types.
The instincts of the Enneagram are often referred to as survival instincts. The three instincts are self-preservation (sp), sexual (sx), and social (so). There are two ways that instincts may be used with the types.
The first produces three subtypes or variants for each type based on which instinct is dominant, the self-preservation subtype, the sexual subtype, and the social subtype (e.g., for type 1 the subtypes would be sp 1, sx 1, and so 1).
The second approach to using the instincts is called "stacking" where all three instincts are seen in an order of preference. For example, your preferential order might be sexual 1st, social 2nd, and self-preservation 3rd. This would be written sx/so where the 3rd instinct is presumed by its omission.
While the subtype approach creates 3 variations of each type, the stacking approach creates 6 variations of each type. That's 27 to 54 variations for all nine types depending on which approach is used.
While wing, tri-center, and instinct variations can be used separately, they're often used in combination. If you use all three in combination then there can be up to 216 variations for each type or 1,944 variations for all nine types.
While 9 types aren't really enough to describe personality, 1,944 variations may be more than enough. To avoid being overwhelmed, it's best for someone new to the Enneagram to start with the basic 9 types before exploring the variations of type.