Help

Click on the "Contact Us" button located on the left of this answer.

Prices on this website reflect suggested retail prices. All customers are awarded a discount off the listed prices. Discounts vary depending on the customer and product. Customers can contact the office for an explanation of our discount system, and their individual discount.

High speed steel drill bits are the most widely used of all metal cutting tools and are the most indispensable mechanic’s tool. The three principal parts of a HS Drill bit are the shank, flutes, and point.

In order to use a drill bit you lock the shank in the chuck of the power tool and then force the point of the drill bit against the work so the cutting edges of the point (the cutting lips) bite into the material. During cutting the chips of the material will curl and exit through the flutes from the hole.

In order for a drill bit to remain sharp under the high temperatures generated by drilling it must be made of high speed steel. Only high speed steel has sufficient alloys to withstand frictional heat up to 1000° F without softening. DESCO has available Cobalt drill bits that are made of special high speed steel plus a significant percentage of cobalt. This alloy adds high hardness and abrasion qualities plus superior resistance to heat. However, due to their hardness, cobalt drills are more brittle than high speed steel drill bits and their use should be reserved for extra tough or production drilling. Cobalt drill bits are excellent for drilling stainless steel.

Drill bit sizes fall into four categories: fractional, wire gauge number, letter, and metric. The decimal equivalents of these various diameters can be found in the chart on page 72 of our DESCO catalog. If you check this chart you will see that the number and letter sizes provide additional size choices between the fractional sizes.

Fractional – Fractional size drills range in diameter from 1/64” to 4” or larger. The sizes increase by 64ths in the smaller sizes, by 32nds and 16ths in the larger sizes.

Wire Gauge Number – Numerical size drills are numbered from 1 to 80, the numbers corresponding to wire gauge sizes. All are smaller than ¼”, ranging in diameter from .0135” (No. 80) to .2280” (No. 1). Note that the lower the number, the larger the drill. Wire gauge sizes are used where more exact sizing is required below ¼”, such as tap drills.

Letter – Letter size drills from A to Z begin where Number Drills end (.2340” to .4130” diameter). They are used where more exact sizing is required in larger sizes.

Metric – Metric size drills are designated in millimeters. 1mm = .0394” and a 1” drill = 25.40mm. A decimal equivalent chart, such as the one we include with our drill sets or the one found at the back of our DESCO catalog, may be used when converting to metric drill sizes.

Types of Shanks

We offer drill bits in straight shank and reduced shank styles. Straight shank refers to the fact that the shank end of the drill bit, the part that goes into the drill chuck, is the same diameter as the rest of the drill bit. A reduced shank drill bit has the shank end reduced in diameter so that the drill bit will fit standard chucks.

The chucks on portable electric drills and drill presses will normally accommodate shank sizes of 1/4”, 3/8”, or 1/2”. They will therefore accept straight shank drill bits up through their chuck capacity. In order to drill holes larger than the chuck capacity we offer drill bits with reduced shanks. Our 1/4” reduced shank drill bits go up through 1/2” in diameter, our 3/8” reduced shank drill bits go up through 3/4” in diameter, and our 1/2” reduced drill bits go up through 1-1/2” in diameter.

Jobbers Length Drill Bits. Most drill bits come in standard lengths called Jobbers Length. These drill bits are used for all general purpose drilling. However, there are a variety of other lengths available.

Screw Machine Length Drill Bits. These drill bits, also called “stubbies” or stub length drills, have short flutes and a short overall length. This design gives them maximum rigidity to resist breakage. They are generally used in sheet metal.

Double End Drill Bits. These drill bits also have short flutes and a short overall length. They are used in drilling sheet metal, auto body repair, storm windows, and similar drilling jobs.

Extra Length Drill Bits. We offer 6” and 12” overall length aircraft extension type drill bits for drilling 1/16” to 1/2” holes through walls and partitions for wiring of electrical outlets, stereos, televisions, appliances, etc. They are also ideal for use in automotive or general purpose machinery work for drilling in hard to reach areas.

Longboy Drill Bits. These are available in 12” and 18” overall lengths. They have longer flutes than aircraft extension bits and are available in larger diameters, either straight shank or 1/2” reduced shank.

Plexiglas Drill Bits. These bits have extra sharp 60° points with more cutting surface for clean cutting and drilling in plastic materials. Drill bits with standard points tend to crack plastic materials, so the use of these specialized plexiglas drill bits is recommended.

Taper Length Drill Bits. These bits are a little longer than jobbers length drills.

Drill bits can have different point angles. The point is the cutting tip. The standard point angle is 118°. This point angle is a general purpose angle and works okay in a wide range of materials such as wood, steel, and aluminum. It is normal to use a punch to make a small impression where you want to start drilling with this kind of point, since the point may “walk” around on the surface if it doesn’t have a small depression to help it get started in the correct location.

We offer an optional point called a 135° split point on our heavy duty drills, cobalt drills, titanium drills, screw machine length drills, and 6” and 12” aircraft drills. The 135° point tends to form its own hole and therefore no center punch is required. Splitting the point creates a pair of secondary cutting edges allowing the drill to start cutting immediately on contact with the work. This prevents point skidding, requires less pressure and makes it easier to start drilling. Split point drills are excellent for drilling holes in sheet metal and in places where work cannot be held firmly in place. The flatter 135°point is also best for drilling hard, tough materials.

Before drilling a hole in metal, it is always advisable to locate the hole position with a center punch. This will prevent the drill from “walking” and damaging the surrounding surface. Insert the drill in the drill chuck by twisting the drill and at the same time hand tighten the chuck to properly “seat” the drill. Then tighten the chuck securely so the drill is locked in place before drilling. When drilling most metals, a generous application of cutting oil is necessary to obtain the best drilling results, prevent overheating of the drill bit and prolong its useful life.

Whenever possible, the RPM of the drill bit should be tailored to suit its diameter. For example, when drilling mild steels and metals, the correct speed for a ¼” drill would be approximately 2pp RPM. However, when drilling a ½” hole, the speed should be reduced to about 600 RMP. Most drill presses and today’s portable electric drills with their variable speeds are ideally suited for these necessary speed changes. For larger diameter drill bits and for drilling hard and tough steels, reduced the drill speed not only prolongs the life of the drill but will product a more accurately drill hole.

Pressure on the drill point is very important. A steady, even pressure should always be used when feeding the drill. A slightly curled continuous chip should be produced when the drill is properly fed. Care should be taken not to over feed or use too much pressure on small diameter drills since it is possible to break them. The drill bit should be partially withdrawn periodically to clear chips from the hole and to allow more cutting fluid to be added. This is especially important when drilling deep holes. A hole greater than four times the drill bit diameter is usually considered a deep hole.

Using the correct drill size is very important. Trying to enlarge an existing hole beyond the diameter of the drill bit being used is definitely not recommended. This will damage or break the drill bit and cause premature wear on the power tool itself. There is a standard drill size for practically any hole requirement, so select the right one. Drill size is extremely important, especially when drilling a hole for thread tapping.

Always use a sharp drill bit. DESCO drill bits are precision made and their drill points ground to close tolerances. Drill bits can be re-sharpened many times throughout their service life. However, a drill sharpening machine or fixture is required to properly restore the accuracy of the drill point and its cutting edges.

Masonry drill bits are tipped with a special ultra-hard metal called Tungsten Carbide for drilling in concrete or masonry materials. Any portable electric drill or drill press can be used. Normal speeds are satisfactory for drilling the usual masonry materials. However, use lower speeds when drilling extremely hard or very abrasive materials. DESCO masonry drills come in many sizes and lengths depending on the application.

To drill holes up to 3” diameter, a core drill bit is used. These are multi-carbide tipped masonry drills. Because core drill bits have larger hexagon shanks, the use of a special portable electric drill is usually required.

No other method of holding things together offers the flexibility of threaded parts which can be assembled or taken apart with equal ease. You can easily cut threads up to one inch in diameter in most metals with hand tools called Taps and Dies. Just as a drill bit cuts material away to make a hole, Taps and Dies cut material away to make a thread.

Taps are used to cut threads on the inside of a hole, as in a nut. One end of the tap is square so it can be turned with a tap wrench. As the tap turns, it bites into the metal, removing material which flows into the flutes. To form the thread, the hole must be smaller than the outside diameter of the bolt or screw that fits it. In order to cut, the point of the tap is chamfered, or tapered, with the cutting edge higher than the back edge.

There are three basic styles of taps:

Taper Taps have 8 to 10 threads chamfered for easy starting and are used for tough threading jobs.

Plug Taps are used for ordinary threading and have a 3 to 5 thread chamfer, or relief, at the point.

Bottom Taps have a short chamfer of 1 to 1-1/2 threads. They are used where the thread must go to the bottom of a hole.


DESCO offers carbon steel and high speed steel taps. Carbon steel taps are more economical and suitable for ordinary use. High speed taps are made from more expensive and more durable high alloy steel and thus are suitable for volume production.

DESCO offers high speed steel taps in two classifications: cut thread and ground thread. A cut thread tap is made by rolling the thread. This is the same process by which a carbon tap is made. This gives a smooth accurate thread that is resistant to breakage.

A high speed steel ground thread tap is made through a precision grinding process to extremely fine tolerances. HS ground thread taps are more expensive than either carbon or high speed steel cut thread taps, and they are used primarily in manufacturing high precision products.

First, measure the thread on the screw or bolt you intend to use. You can use a micrometer to measure the outside diameter and a screw pitch gauge to measure the number of threads per inch. If a screw pitch gauge is not available, a scale can also be used by counting the number of threads to an inch (or in a half inch and then multiplying by two).

Second, determine the correct size hole to drill before tapping. This is known as the tap-drill size. Tap drill sizes are usually computed for a 75% full thread which is as strong as a 100% full thread and does not put undue strain on the tap. The correct tap drill in each case can easily be found in the DESCO tap and drill pocket chart or in the chart appearing in the back of the DESCO catalog.

After the hole has been drilled, clamp the work in a vise with the hole in an upright position. Apply a good grade of cutting oil to the tap. Grasp the tap wrench with your right hand directly over the tap, or with both hands close to the tap, and place the tap in the hole. Press and start to turn the tap clockwise into the hole. Turn the tap forward until resistance is felt and then turn the tap a quarter-turn backwards to break the chip. This will cause the teeth of the tap to take a firm hold in the side of the hole. Make sure the tap is square with the surface of the work.


Once the thread is started properly, the tap will draw itself into the work and downward pressure is no longer needed. Grasp the wrench by both handles and with a slow, steady movement, continue turning the tap into the hole, backing up occasionally (when increased resistance is felt) to allow the chips to break. Never force a tap because it can become so tightly wedged that it will break. Using too much pressure and letting the tap get out of line will also break the tap.

Dies are just the opposite of taps in that they cut external threads on the outside of pipes, rods or bolts. The die is held in a Die Stock and worked in much the same manner as a tap.

DESCO offers different types of dies such as 1” solid round, 1” hexagon, 1-7/16” hexagon, 1-7/8”, and screw adjusting round dies in 13/16”, 1”, 1-1/2”, and 2” sizes.

With screw adjusting dies you can cut threads oversize for a tight fit and undersize for a loose fit. Adjustable round dies have a setscrew in the edge of the die and the thread fit adjustment is made in the die before locking it into the die stock.

Hexagon dies are not adjustable but they can be used where there is no room for a die stock. Threading can be accomplished with an open end wrench, socket wrench, adjustable wrench, or hexagon die stock if space permits.

Hexagon Rethreading Dies are extra thick giving more cutting edges to restore damaged threads.

Left Hand Dies are available for cutting left hand threads.

Pipe Dies are used for cutting pipe threads.

First, before starting to cut a thread, make a small bevel on the edge of the rod or pipe to be threaded. This makes starting easier. Fasten the work in a vise, either vertically or horizontally, depending on the length of the piece. Grasp the die stock with both hands near the die and place the starting side of the die over the end of the rod or pipe. Apply a good grade of cutting oil. Press down firmly on the work and at the same time slowly turn the die clockwise, backing up when resistance is felt just as you do with a tap. Be sure the die goes on square.


After the thread is started, grasp the die stock by both handles and, with a steady forward and back movement, continue turning the die onto the work, advancing only slightly with each turn. It is no longer necessary to press down because the die will draw itself onto the work when the thread is started.

Even when the fit of a threaded hole is good, bolts or screws sometimes break off in the hole when you apply too much pressure in tightening or when you try to remove a jammed or badly corroded part.

A broken bolt or screw maybe removed from a hole with a screw extractor.

First, drill a hole in the broken bolt. The correct drill size to use is shown on each screw extractor and in the DESCO catalog.

Second, insert the screw extractor in the hole and, with a tap wrench, turn counter-clockwise. The screw extractor acts like a corkscrew. It grips into the sides of the drilled hole and removes the broken part on its own threads without damaging the threaded hole.

DESCO offers two types of screw extractors: Left Hand Spiral Tapered Flute and Straight Tapered Flute. The left hand spiral tapered flute is generally recommended for use on steel because of its extra gripping qualities; the straight tapered flute is recommended for soft, ductile metals and materials or for removing threaded tubing or pipe.

The quickest and most exact way to find the number of threads per inch on a bolt or a nut is with a screw pitch gauge. Try different blades of the gauge on the threads until you find the one that matches exactly. The number stamped on the blade is the pitch.

The screw pitch gauge for U.S. threads measures the “pitch” or number of threads per inch.

The screw pitch gauge for metric threads measures the “pitch” or distance between threads in millimeters. Metric threads are measured from one thread to the next. For example, a 6mm – 1.00mm thread is 6mm in diameter and has 1mm between threads.