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bits are available in a wide choice of tooling materials and lengths with the variations targeting specific projects. 

The standard twist drill bits used for drilling aluminum are made from HSS and have a 135° split point. Drill bits for titanium are made from cobalt vanadium for increased wear resistance. 

## Drill Bit Sizes 

Drill diameters are grouped by three size standards: number, letter, and fractional. The decimal equivalents of standard drill are shown in Figure 4-47 . 

## Drill Lubrication 

Normal drilling of sheet material does not require lubrication, but lubrication should be provided for all deeper drilling Lubricants serve to assist in chip removal, which prolongs drill life and ensures a good finish and dimensional accuracy of the hole. It does not prevent overheating. The use of a lubricant is always a good practice when drilling castings, forgings, or heavy gauge stock. A good lubricant should be thin enough to help in chip removal but thick enough to stick to the drill. For aluminum, titanium, and corrosion-resistant steel, a cetyl alcohol based lubricant is the most satisfactory. Cetyl alcohol is a nontoxic fatty alcohol chemical produced in liquid, paste, and solid forms. The solid stick and block forms quickly liquefy at 

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