The Extension Sections are the base uints of the poles. The K-EX20 is the base section from the K-102, the K-EX30 from the K-152, the K-EX40 from the K-202 and the K-EX50 from the K-251. The K-EX60 is 10 inches longer than the base section of the K-251. It is simple to swap base sections, or to replace base sections with extension sections to accommodate special requirements.To specify these special poles simply take the pole, subtract the corresponding extension section and add the longer one. For example: a popular pole is the K-102CC with the base section from a K-152.It is specified as follows: (K-102CC * Deduct K-EX20 * Add K-EX30).The K-102CC already includes the K-CC so don't add it, but remember to add the K-PH or K-T if it is needed.Another popular pole in the feature film industry is based on the K-202, but with the longer base section of the K-251. This makes an easy to handle pole nearly 18 feet long.It is specified as follows: (K-102 * Deduct K-EX40 * Add K-EX50).You will probably want to internally wire the pole so add the K-FT and the wiring. Available in five sizes: K-EX60 (5' extension section) K-EX50 (4' 2" extension section) K-EX40 (3' 4" extension section) K-EX30 (2' 6" extension section) K-EX20 (1' 8" extension section)