![]() Compared to the minor-diameter specifications for a 1/4-20 UNC-2B tap (0.1960"- to 0.2070"-dia.), the finished hole size is near the high limit, 0.0022" under the maximum minor diameter (Table 2). This would result in a drilled hole size of 0.2048", approximately 70% of thread height. 7 (0.2010"-dia.) drill will, on average, produce a hole that is 0.0038" larger than the drill’s diameter. This became known as the "probable hole size," which is often listed on tap/drill charts next to the decimal equivalents of the drill sizes (Table 1). Advanced drillpoint geometries, new flute shapes, coolant holes, improved HSS and carbide grades, and coatings like TiN and TiCN have done much to improve the quality and size of the drilled hole.Īs drill recommendations were being developed for standard-size coarse (UNC) and fine (UNF) series threads, drill sizes were selected based on tests showing that a standard, general-purpose, jobber-length drill - having a standard 118° point angle - will produce a hole size larger than the measured drill diameter. Most importantly, the drills used to make the holes to be tapped have improved. Many changes have taken place in the years since tap/drill charts were first developed - programmable machinery, rigid tapping, synchronous tapping, better toolholders, specialized tapping fluids, and premium high-grade taps. The problem is, that factor can’t be calculated accurately using traditional tap/drill charts. While many factors contribute to tap failure or breakage, one basic, obvious factor is often overlooked - the size of the drilled hole. See Supplemental Topics for Anchors or visit for more corrosion information.The key to successful tapping is knowing the true size of the drilled hole. Not for use in other corrosive or outdoor environments. Intended for some pressure-treated wood sill plate applications. Mechanical galvanizing meets ASTM B695, Class 65, Type 1. Titen HD® Anchor Product Data - Mechanically Galvanized using a torque wrench, driver drill or cordless 1/4" impact driver with a maximum permitted torque rating of 100 ft. * These models do not meet minimum embedment depth requirements for strength design and require maximum installation torque of 25 ft. Titen HD® Anchor Product Data - Zinc Plated Length of anchor is measured from underside of head to end of anchor. Models THD37134H and THD37212H do not meet minimum embedment depth requirements for strength design and require maximum installation torque of 25 ft. Larger holes are not required for wood or thinner cold-formed steel members. Suggested fixture hole sizes are for structural steel thicker than 12 gauge only. Tighten the anchor into the base material until the hex-washer head contacts the fixture.Insert the anchor through the fixture and into the hole.(Overhead installations need not be blown clean.) Alternatively, drill the hole deep enough to accommodate embedment depth and the dust from drilling and tapping. Drill the hole to the specified embedment depth plus minimum hole depth overdrill (see table below) to allow the thread tapping dust to settle, and blow it clean using compressed air. Drill a hole in the base material using a carbide drill bit the same diameter as the nominal diameter of the anchor to be installed. ![]()
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