Drill Bit For Challenge - Diameter: 1/4" (6mm) x 2 1/2" - CHT stands for chemicals, heat and time. These drill bits are coated in PTFE to prevent buildup and increases the life of the bit. Works great for coated stocks. - CHT: PTFE coated “CHT” bits last longer and run cooler. They cut through tag board, recycled papers and heavy coated stocks without gumming up.