There are four different types of newel posts for stairs; standard newels, landing newels, pin-top newels and stabilizer newel posts.
Standard Newel Posts
The standard newel post is your typical block top newel post that is used in a post-to-post system. These are used when your handrail will be at the same height throughout your railing system.
Landing Newel Posts
Landing Newel Posts are used when ever you have a level change, such as a middle or upper landing, and the handrail changes the height. The block top on the landing newel is usually 13 inches tall.
Pin-Top Newel Posts
Pin-Top newels are used in an over-the-post system where your handrail appears to have a continuous run, or just at the bottom with a volute, turn-out or start easing with cap. There is always some sort of handrail fitting that sits over a pin-top newel.
Stabilizer Newel Posts
The stabilizer newel is used to provide extra support in a long run of railing where a fitting can not be used.