The distance between the floor and the ceiling is 87a€? so which size should I use and is it comes with the upper and lower caps ??

Hello, Thank you for your interest in the Fypon PVC 3/8" Non-Tapered Vinyl Column Wraps. These column wraps do come with a cap and base. Based on the information provided, these column wraps may not work for your application. The two sizes 87" falls between are 72in. and 96in. Fypon advises that the column wraps are field adjustable up to 3in. We apologize for the inconvenience. Thank you again and have a great day!

What are the advantages of 3/8" vs 5/8" Fypon Non-Tapered Column Wraps

Both are essentially the same in its benefits such as durability, but the 3/8 is slightly smaller making it better for a tighter application such as next to a porch or wall.

they say for 4x4 post but wont the 8" work for 6x6 post?

Hello, we will have the description corrected. Thank you for bringing it to our attention. For further clarity, see below: 6" shaft width has an inside width of 3-1/2" 8" shaft width has an inside width of 5-1/2" 10" shaft width has an inside width of 7-1/2" Please let us know if you have further questions. Thank you!