Formatt Hitech Limited HT85ND2.1 85x85MM (3.35-InchX3.35-Inch) Neutral Density 2.1 (7 Stops) Filter for Cokin P Hitech filters are made from the highest quality 1.5mm optical resin. the filter is also available in 100mm, 150mm and 165mm sizes. the 85mm size is useable with Hitech 85mm holder systems or any 85mm (3.35-Inch/Size) holder.