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Different Jobber Drill Bit Sizes And Common Drill Bit Terms

by RockHard Toolz June 26, 2019

Different Jobber Drill Bit Sizes And Common Drill Bit Terms

common drill bit terms



Drill bits are the cutting tools of drilling machines and they can be made in any size to order. Jobber drill bit is the most common type of drill bit that can be purchased in the market today. Generally, the length of a jobber flute is 8-12 times the diameter of the drill bit. And it what makes a jobber unique.  On this article we will be talking about the different jobber sizes and the different common terms of drill bits. 

In purchasing a jobber, there are different material, manufacture, and sizes available. The sizes can be a bit confusing so here's your guide to make it easier. Fractional, Metric, Letter, and Wireall refer to the measurement systems used for Jobbers of regular length. In other words, it's just different ways to describe how wide the bit is.

Fractional Bit Sizes - This drill bit measure bit size in increments of 1/64 inch up to 1 inch, 1/16 inch to 3 inches, 1/8 inch up to 3 1/4 inch, and just one more 1/4 inch increment to 3 1/2 inches. The length of the bit size is recorded as irreducible fractions.

Number and Letter SizesThrough numbers and letter sizes you can have sizes 1 through 80 or A though Z. Wire sizes are another set of measurements starting at 1 and then increasing by whole numbers. 

Remember also that Mechanics Length, Reduced Shank, and Screw Machine Length all refer to the length of the jobber. A Mechanics Length set is shorter in the flute than the average jobber. Because of its strong foundation it can drill through harder materials. For woodworkers jobber length is what they preferred in drilling through woods. Screw Machine Length is more like the Mechanics Length that has a shorter flute. Meaning they are less likely to snap during use, but will drill shallower holes. 

Now that you know about drill bit sizes, as workers it is also important to know the different terms used in referring drill bits. These will add up in our vocabulary so we can have wider knowledge especially if specializes on working in different industries. 

If you are working with people in any specific industry and you notice that they use a specific jargon or certain words that are industry specific. For those who are new to tool industry, these words might seem confusing and may leave you a little puzzled. I hope that the following terms will help you. 



Drill Bit Axis -  This is the imaginary line that forms the lengthwise Center of a drill bit. 


Drill Body– This is the part of a drill bit from the shank to the outer edges of the cutting edge.


Body Clearance Diameter– This is the portion of the land that has been cut away so it will not bind against the walls of the hole. 


Chip Removal– This is the ability of a drill bit to pull material that has been cut away from the point, up the flutes of the drill and out of the hole. 


Chisel Edge– This is the edge at the end of the web that connects the cutting tip.


Chisel Edge Angle– This is the angle between the chisel edge and cutting tip when viewed from the end of the drill bit. 


Cobalt Steel– This is a heat resistant steel that preserves the life of the drill bit. 


Drill Diameter– The diameter over the margins of a drill bit, measured at the point

Feeds– these are determined by the drill diameter, machinability of the material and depth of the desired hole. Small drills, harder materials and deeper holes needs considerations in selecting proper feed rates. 


Flute– This is the groove cut in the body of the drill bit to provide cutting surfaces and it permits removal of chips and allow cutting fluid to reach cutting surfaces. 


Flute Length– the distance from the outer edges of the cutting tip to the long back of the flutes. 


Helix Angle The angle formed between the leading edge of the land and the axis of the drill bit.


Lip The cutting edge of a  two flute drill bit  which extends from the chisel edge to the outer edge.


IPR– Inches per second (The feed rate)


IPM– Feed rate in Inches Per Minute.  IPS (Inches per Revolution) x RPM (Revolutions per Minute)= IPM


Neck– The section of reduced diameter between the body and the shank of a drill bit.


Land – The outer portion of the body of the drill bit between two adjacent flutes.


High Speed Steel– The high quality steel used in drill bits to maintain maintenance and improve industrial applications


Overall Length– The length from the end of the shank to the outer corners of the cutting lip.


RPM– Revolutions Per Minute.  RPM= (SFM(Surface Feet per Minute) / Dia) x 3.82


Point– The cone-shaped cutting end of a drill bit, made from the ends of the lands and the web.


Split Point– A split point drill has a special point configuration that eliminates “walking” so holes stay center.


Point Angle– The angle of the cutting surfaces on a drill point, commonly 118 deg or 135 deg.


Shank The part of the drill bit that is held driven.


SFM– Surface Feet Per Minute.  SFM= RPM x Dia x .26


Size– Measurement reference for the diameter size of a drill bit.  Drill bit size is usually expressed as either fractional, wire, letter or metric.




What measurement system you choose is really up to you and the job you’re working on. And I hope that this article will guide you and gives you more helpful knowledge. For more drill bit information just visit  https://rockhardtools.myshopify.com/

RockHard Toolz
RockHard Toolz

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