 Tri-X 400 is the more common of the two, available in 24- and 36-exposure rolls of 35 mm and rolls of 120 as well as 50 and 100 ft bulk rolls of 35 mm.Tri-X 320 is available in 4×5", 5×7", and 8×10" sheets.Tri-X 400 is usually rated at ISO 400 when processed in standard developers and remains among the fastest black and white films today.