This TDP upgrade kit will work with all versions of the TDP. These all-weather pen refills write on wet paper and upside down in all weather conditions. This ball point refill was jointly developed with Rite-in-the-Rain and the Fisher Space Pen Company as a pressurized ball point refill with waterproof ink and will work in temperatures ranging from -30F to 250F. These pen refills work in conjunction with the Rite in the Rain paper notebooks also sold by MIL-TAC for an all weather combination for military, law enforcement, and outdoor sport enthusiasts to make sure that your notes are permanent and available.