These cardboard mason bee nesting tubes are 6" long and 5/16" diameter, which is considered the ideal size for the mason bee. You can use the tubes without liners but cleaning them out is difficult. It is far better to use the paper liners. At the end of the season, you pull out the liners that are filled with cocoons and store them in a safe cool place for winter. And you can then reload fresh empty liners in the tubes for the next season. You will need to reinstall the liners with cocoons into you nest box. Alternativey, you can remove the cocoons from the liners to clean them and then install them into the nest box the following season.