The Difference Between Jobber Drill Bit Sizes

The Difference Between Jobber Drill Bit Sizes

I love the word Jobber.  Seriously, say it out loud right now.  I’ll wait.  Jobber.  Hilarious.

But they are also wonderful, useful tools.  They are probably the most common type of drill bit on the market today.  Generally speaking, the length of a jobber flute is 8-12 times the diameter of the drill bit.  That’s what makes it a jobber.

It also refers to someone who is contracted to lose a professional wrestling match, but that’s another post entirely.

When shopping for a jobber, there are a wide variety of material, manufacture, and sizes.  The sizes can be especially confusing, so here’s a quick rundown.  Fractional, Letter, Metric, and Wire all 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 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 ¼ inch, and just one more ¼ inch increment to 3 ½ inches.  The length of the bit size is recorded as irreducible fractions (Such as 1 7/32 instead of 39/32).

Number and Letter Sizes measure their bits in…well…numbers or letters.  In other words you can have a size 1 through 80 or a size A through Z.  Wire Sizes are another set of measurements starting at 1 and then increasing by whole numbers.  Metric uses standard metric measurements.

Mechanics Length, Reduced Shank, and Screw Machine Length all refer to the length of the Jobber itself.

A Mechanics Length set is shorter in the flute than the average Jobber.  It’s sturdier because of this, and is better for drilling through harder materials.  Jobber length is usually preferred for drilling through wood.  Reduced Shanks pretty much self explanatory.  The shank is shorter to fit into certain machines.  Lastly, Screw Machine Length, like the Mechanics Length, will have a shorter flute.  This means they are less likely to snap during use, but will drill shallower holes.

What measurement system or flute size you choose is really up to you and the job you’re working on.  What measuring system is easier for you to use?  Do you need to drill a deeper hole, or are you more concerned with durability?  You can also purchase a handy conversion chart, or there is a very good one here:

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One Response to “The Difference Between Jobber Drill Bit Sizes”

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