Thread percentage: (77% thread is what you want to use) A 100% thread is 3/4 qtr, or (6/8 th), of the full 60° triangle which is the maximum allowed height of a full thread, the "V" shape, including flats. NOTE: The tap drill size of a hole that will be cold form tapped is usually bigger than it cutting tap counterpart. These taps have no "flutes" and are usually oval shaped or not quite round. Form tap: (Cold forming tap) A tool that makes the helical portion of a threaded hole by forming, or deforming, the material as it moves along a predrilled hole. They should be used in that order when tapping holes that do not break through. Cutting taps usually have sharp "flutes", somewhat like the spirals of a drill, where the chips can accumulate and be ejected out of the hole NOTE: Cutting taps come in sets of 3 A starter tap, a midway tap, and the bottoming tap. Cutting Tap: A tool that makes the helical portion of a threaded hole by cutting material as it moves along a predrilled hole. NOTE: Most basic sizes have a coarse and a fine series of thread. Pitch: (Distance between each thread, or "V"s.) The distance the a screw or nut will advance every 360° turn. NOTE: If the length of the threaded portion of a screw or threaded hole is shorter or longer than one inch, the size of the "V" shape is still defined by the number of thread that would fit along a one inch length. TPI: (Threads per inch) The number of thread, or "V"s along a one inch length which in turns, defines the size of the "V" shape of the helical portion of a thread. NOTE: The size of the hexagon of a bolt or nut has no relevance when defining a thread size. The biggest external diameter of a Screw or the biggest internal diameter of a threaded hole. Outside diameter: This is the biggest diameter of the helical portion of a thread. NOTE: The American Metric UN thread standard is compatible with the international ISO Making a thread that follow these specifications will ensure that it will work with threaded holes or shafts made by other manufacturers that follow theseĬommon specs. Metric UN: (American Metric Unified National thread form) A standard that describes the shape of an internal or external thread using Imperial UN: (Imperial Unified National thread form) A standard that describes the shape of an internal or external thread using imperial inch dimensions. Percentage of Full Thread X mm Pitch size (mm) of Thread (mm) *Note: Drill size should be smaller than hole size by the probable amount the Drill will cut oversize.Glossary TDS: (Tap drill size) The size of the hole that must be drilled before a tapping operation. of Threads per Inch *Drilled Hole = Basic Major Dia. 01299 Formula For Obtaining Tap Drill Sizes For Thread Forming Taps: * Drill Hole = Basic Major Dia.0068 x Percentage of Full Thread size (inches) of Thread (inches) No. Selected Percentage of per Inch x of Thread Drill Dia. of percentage of full Thread = Drilled Hole* of Thread No.Ģ Of threads per inch size Note: Select nearest commercial stock of Full Thread for Other Drill Sizes No. However, variations in material and equipment may require the use of drills which are larger or smaller than those : Minor Diameter Limits for steel, plastic, and magnesium are such as to allow for material contraction and provide maximum tap for Obtaining Tap Drill Sizes for Cutting Taps: Major Dia.01299 X Amt. : Tap Drills listed above should produce holes within the required limits. OFTAPDRILLTAP DRILLDRILLTAP DRILLSIZESIZE(INCHES) (INCHES) - 40# - 40# - 32# - 40# - 32# 24. max.ġ & Dies199 Tap Drill Sizes STI ( screw Thread insert ) TapsALUMINUMSTEEL, PLASTIC, MAGNESIUMDECIMALMINOR (AFTER TAPPING)DECIMALMINOR (AFTER TAPPING)STITAPEQUIV. of tap drill tap drill drill tap drill size size (inches) min. limits (after tapping) decimal minor dia. Tap drill sizes – sti (screw thread insert) taps aluminum steel, plastic, magnesium decimal minor dia. of percentage of full Thread = Drilled Hole* of Thread No. & Dies199 Tap Drill Sizes STI ( screw Thread insert ) TapsALUMINUMSTEEL, PLASTIC, MAGNESIUMDECIMALMINOR (AFTER TAPPING)DECIMALMINOR (AFTER TAPPING)STITAPEQUIV. Example: bankruptcy Search Tap Drill Sizes – STI (Screw Thread Insert) Taps
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