Bass Drum O's Bass Drum Port"O" Green Chrome 6 in. Replicating the original bass drum hole reinforcement, these have a snap on design and are available in different sizes and colors to suit your application Replicating the original bass drum snap-on design reinforcement system, Bass Drum Os add durability and pizzaz to ported bass drum heads Simply snap the O on the port hole to give a finished appearance to your bass drum Replicating the original bass drum snap-on design reinforcement system, Bass Drum Os add durability and pizzaz to ported bass drum heads Simply snap the O on the port hole to give a finished appearance to your bass drum