1. Base-Closed extensions are populare for EU market. 2A, 3A with 6mm steel plate; 4A with 6mm thickness steel plate. 2. Base-opened extensions are popular for North America. Light duty for 2A, 3A forks. 3. The length of extensions should not exceed 150% of the forks. For example, the forks are 1200mm, then the Extensions should be less than 1800mm.