PolarPro 77mm ND16 QuartzLine Solid Neutral Density 1.2 77-ND16
NiSi SWIFT ND16 (4 Stop) Filter for 77mm True Color VND and Swift System | NiSi Optics USA
Amazon.com: NiSi 77mm Swift System Add-On Kit | Swift Adapter Ring, Two Friction-Mounted Filters (ND16 4-Stop, Black Mist 1/4) | Stack Filters On True Color VND or Separately on Lens | Photography
77mm Neutral Density ND ND16 Filter 4 Stops (1.2) Optical Glass Lens For Camera | eBay
Ice 77mm ND16 Solid Neutral Density 1.2 Filter ICE-ND16-77 B&H