OEM Systems RIR-815 Rough-In Kit for AP815LCRS and PS815LCRS: * Mounting straps span 24" members * Dome/mounting flange slides along straps * Substantial friction holds ring fast * Inexpensive * Versatile * Wire inlet * Shields speaker for insulation * Metal straps span 24" centers * For all 8" in-ceiling round 15-degree models * Mouth opening: 11-1/2" round