40pcs Metric Tap and Die Set, Metric Standard Rethreading Tool Kit with Thread WrenchTaps: Taps are used to cut internal threads, typically into pre drilled holes. They come in various sizes and thread pitches to match the desired thread specifications. A tap set may include both taper and bottoming taps to facilitate thread cutting in different situations. Dies: Dies are used for cutting external threads, usually on rods or bolts. Like taps, they come in various sizes and thread pitches to match the desired specifications. A die set