Recessed flange for pole-mount.
Upgrade your subwoofers! Replace existing 1 3/8" sockets with the SSA20M threaded speaker adapter. Designed to be a direct replacement for most socket mounts; simply remove and replace. M20 threading provides a rock-solid, wobble-free connection between the subwoofer and compatible speaker poles. Perfect for use with the SS7746 Adjustable Subwoofer Shaft.