Unit 9 Holes 141 Copyright Goodheart-Willcox Co., Inc. The second line specifies information for the coun- tersunk hole in the following order: the countersink symbol, the diameter symbol, the size of the counter- sink diameter, the “by” symbol (the letter X), and the included angle of the countersink. Counterdrilled Hole Counterdrilling is the process of drilling a coni- cal-shaped hole to a specified depth to allow a fas- tener’s head to sit at or below the part’s surface. A counterdrilled hole is similar in appearance to a coun- terbored hole, except the bottom of the hole has a con- ical shape. Counterdrilling does not require a noted angle because the drill’s angled point shapes the hole. The typical angle produced by a drill is 120°. The specifications for a counterdrilled hole appear on two lines. See Figure 9‑11. The first line spec- ifies information for the small hole in the follow- ing order: the diameter symbol, the size of the small hole diameter, the depth symbol, and the depth size (the depth symbol and depth size are only included if required). The second line specifies information for the counterdrilled hole in the following order: the diameter symbol, the counterdrill diameter size, the depth symbol, and the counterdrill depth. There is no symbol for counterdrill. Spotfaced Hole Spotfacing is the process of providing a smooth, flat surface around a hole. A rough surface, such as a casting, is spotfaced to accommodate the seating of a washer or bolt head. Spotfacing also provides a flat seat on an inclined surface. The machining processes for spotfacing and counterboring are the same, except for the depth of the spotfaced hole. Spotfacing produces a shallow, recessed surface approximately .0625″ deep. The spotface symbol is the counterbore symbol with the letters SF inside. In older editions of the ASME Y14.5 Means this Countersink symbol This Goodheart-Willcox Publisher Figure 9-10. Specifications for a countersunk hole. Means this This Goodheart-Willcox Publisher Figure 9-11. Dimensions for a counterdrilled hole.