Having determined the bolt that we want to use in the specific case, we already have a technical specification for the thread which will host it. The drill size chart is a table list standard size drill bits in several measurement systems, including fractional, metric, wire gauge number, and letter. The metric system uses the thread pitch, which is the distance between threads, measured in millimeters. Before you design your next product or make updates to an existing product, consider partnering with Optimas to take advantage of our many capabilities. The taper tap is only used in certain situations such as when the material is very hard or the hole is too small.

The first recorded use of taps in metalworking is placed sometime in the 18th century, while the British engineer and industrialist Joseph Clement popularised the tool in the mid-19th century.

RS PRO straight flute, taper taps are available in a range of sizes from M2 to M20, offering a wide choice to suit various tasks. Some prefer to use somewhat arbitrary but reliable formulas like: “Dtap = Nominal Diameter – Thread Pitch”. They also feature a blue stream tempered finish helping to reduce friction and produce a cleaner thread. A rule of thumb is that the right tap drill is around 85% for coarse threads and 90% for fine threads which feature a higher number of threads per axial distance. When it comes to the selection of drill bit sizes and tap sizes, there are standard drill and tap size chart for reference.

Fractional sizes are listed in inches, metric sizes are listed in millimeters following the letter “M”.The “M” indicates the “metric diameter” of its thread (see tap drill chart below), which in our case is 4 mm. Just a quick note to thank you for an awesome job on my gate shoes, The shoes were millimeter perfect and all the holes in just the right position. mm drill bit, but using that drill would leave an inadequate margin for the creation of the appropriate thread depth. The taper tap features a smooth diameter transition that allows for a less aggressive cutting action. So, if we wanted to drill a hole for our example bolt, we would need to use a drill that is smaller than 4 mm.