Take a look at this item on eBay 😀
The RSS390-PR 15'' passive radiator includes:
(1) Passive radiator
(7) 75 gram disk weights
(1) wing nut (for tuning)
(1) lock nut (for final assembly)
Specifications: • Fs: 18.2 Hz • Vas: 7.51 cu. ft. (212.8 liters) • Qms: 4.01 • Cms: 0.22 mm/N • Mms: 400g • Rms: 12.41 kg/s • Sd: 829.6 sq. cm. • Xmech: 30 mm • Dimensions: Overall diameter: 15.29'', Cutout diameter: 14'', Depth: 4.76''.
https://m.ebay.com/itm/Dayton-Audio-RSS390-PR-15-Aluminum-Cone-Passive-Radiator/222552760883?NAV=HOME