If you are looking for a size beyond the standard 4X4 or 6X6? With these post caps you have a variety of options.
The Victoria Copper High Point is available in 8X8 and 10X10.
The Newport series offers a 4X6 post cap in the High Pyramid and Classic styles.
Newport High Pyramid: Available size: 4X6.
Newport Classic. Available size: 4X6.
All of the above post caps are available in the standard 4X4 and 6X6 sizes.
4X6 post caps have an inside opening of 3-5/8" X 5-5/8".
8X8 post caps have an inside opening of 7-5/8" X 7-5/8".
10X10 post caps have an inside opening of 9-5/8" X 9-5/8".