The WonderPana Classic is a line of all metal filter holders for super-wide angle (SWA) and ultra-wide angle (UWA) lenses that make it impossible to use standard filters. This WonderPana Classic core is only compatible the Sigma 12-24mm f/4. 5-5. 6 EX DG ASP HSM II Full Frame lens. The custom fit of each core prevents any light leak which drastically reducing the possibility of unwanted flare. The Classic core is compatible with a large selection of Foodoir 145mm filters. These include double threaded slim filters such as: ND4, ND8, ND16, ND32, ND100, MC-UV, CPL, MC-CPL. Other filters include single threaded ultra slim ND4, ND8, ND16, ND32, and ND100. The Classic core is also compatible with the WonderPana 66 filter brackets which enable use with Foodoir 6. 6x8. 5in rectangular filters such as: GND 0. 6SE, 0. 6HE, 0. 9SE, 0. 9HE and reverse GND 0. 6SE. Note: No filters are included with this kit. The Core is non-rotating. The rubber 'nubs' on the core do not serve a purpose other than in the manufacturing process, they may be discarded. All pictures are for illustration purposes only. Actual product may vary slightly due to ongoing improvements in design.