This 4 Arm Tree Perc Straight Tube Bong w/ Diffused Downstem gives amazingly smooth hits thanks to its dual perc design. It features an 18mm female joint with an 18mm male to 14mm female removable diffused downstem to begin the filtration process. This 3" diffused downstem has multiple slits at one end, allowing for the percolation of smoke. After the smoke has filtered through the main chamber, the diffusion process continues with the colored glass 4 arm tree perc. A tree perc is a great working perc, each of the 4 arms has diffusion slits, which provides optimal diffusion!