Adapter ring so you can use an aftermarket sub. 6 holes to attach the ring to the box and 8 holes to attach the sub to the ring. The 8 sub holes are 200mm across from each other. I recommend using a higher temp/stronger filament like PETG, ABS or ASA. Sub will most likely hit the speaker grill so you might have to remove that or figure something out to keep the sub from hitting it.