2 1/2 x 7 1/2 Subwoofer Replacement Spider. Some of the models that use this spider include: Any requiring a 7 1/2" spider and a 2 1/2" voice coil. Inside Diameter - 2 1/2"; Outside Diameter - 7 1/2"; Stiffness - "E" on a scale of A-F (F is the stiffest). Inner 3 rings are double layered. Inner mounting has 1/4" tall vertical lip to hug the coil former. Stacking is not recommended.