Please measure your posts before purchase. Please let us know your desired base adapters. Interchangeable black base adapters in different sizes Solar Light Post Cap 2 SMD LED Post Mount. This Fine Solar Post Cap can be used for post or wall mount. Real pebbled printed glass. Material: Heat resistance plastic. On/Off switch (for testing and storage purposes- Must be turned on for initial use) Operating Time: Up to 8 hours (depending on weather, regions and sunlight intensity available) Designed to fit on 4" x 4", 5" x 5", 6 "x 6" posts 6x6 base adapters: Inside diameter of one side is 5.75" (good for wood/composite posts) and inside diameter of other side is 6 1/16" (good for PVC/Plastic/Vinyl posts) Solid/Hollow 5x5 base adapters: Inside diameter of one side is 4.75" (good for wood/composite posts) and inside diameter of other side is 5 1/16" (good for PVC/Plastic/Vinyl posts) Solid/Hollow 4x4 base adapters: Inside diameter of one side is 3.75" (good for wood/composite posts) and inside diameter of other side is 4 1/16" (good for PVC/Plastic/Vinyl posts) Solid/Hollow