Jobber drill bit sizes: what jobber means, and the length chart
A jobber drill bit is the standard general-purpose twist drill: the ordinary HSS bit that hardware-store sets are made of. Jobber is a length class, not a material or a brand, and it is defined by proportion rather than one fixed number: the flute length falls between roughly 9 and 14 times the drill diameter, depending on size [1] [2]. A 1/2 in jobber drill therefore carries about 4-1/2 in of flute, and a 1/8 in bit about 1-5/8 in [1] [3]. This page explains the name, settles the jobber versus regular question, places jobber against the shorter and longer length classes, and carries the full size and length chart for fractional bits from 1/16 to 1/2 in, with every row checked against two independent published tables.
The one-minute answer
Three facts cover most of what people ask. First, a jobber bit is a regular drill bit: the standard-length twist drill that most sets contain [1] [2]. Second, the word jobber comes from the wholesale trade: a jobber was a distributor who bought from manufacturers and sold to retailers, and bits made for the trade settled on a medium length suitable for a wide variety of jobs, so the name became the name of the length itself [2] [3]. Third, when a listing says HSS jobber drill bits and nothing else, the material is high-speed steel and the length is the standard one; nothing about the pairing is special [5] [6].
What jobber means, and where the name came from
Drill makers sell the same diameters in several length series. The one sold as general purpose, in the widest range of sizes, finishes, and materials including high-speed steel, cobalt, and solid carbide, is jobber length [5] [6]. Its dimensional signature is the proportion: flutes 9 to 14 times the diameter (some references quote 8 to 12 times; the tables the chart below is built from follow the ANSI B94.11M jobber series, which places every 1/16 to 1/2 in fractional size inside the 9 to 14 band) [1] [2] [4].
The etymology is commercial, not mechanical. In the period roughly 1850 to 1950, a jobber was a person or company that bought from manufacturers and sold to retailers [2] [3]. Manufacturers producing bits for the trade, rather than to a specialized machining application with its own length requirements, made them of medium length suitable for a wide variety of jobs; jobber-length became the term for that standard, filling the same role the words general purpose and multipurpose fill now [2] [3]. So the name is not about jobber shanks and not about a job shop; it is a wholesale term that stuck to the medium length.
One vocabulary trap: a mechanics length bit is a jobber-style bit made shorter, with shorter flutes and overall length, for more rigidity; Albany County Fasteners, whose explainer is built around the pair, notes the shorter build is considerably stronger and less prone to breakage and shearing, which suits harder drilling [2]. It sits between screw-machine and jobber in practice, and the term mechanics drill bit on its own means nothing precise [2] [3].
Jobber vs a regular drill bit
The question people actually search is whether they need to buy something called a jobber bit separately. The answer is no: the fluted twist bits in a typical indexed set, the ones a hand drill or drill press chuck holds, are jobber length [1] [5]. Wikipedia calls jobber-length drills the most commonly found type of drill [1], and DrillsandCutters opens its jobber chart with the same sentence in retail language: jobber length drill bits are standard size drill bits [5]. A product page that says 1/4 in HSS drill bit with no length class means a 1/4 in HSS jobber bit: 4 in overall, 2-3/4 in of flute [5] [6].
Where the distinction becomes real is the exceptions. Reduced-shank bits (Silver and Deming) carry a big diameter on a smaller straight shank; core bits, SDS masonry drills (see our SDS bit size chart), spade bits, and Forstner bits follow their own length logic entirely. This page covers straight-shank twist drills only.
The length classes: jobber vs screw machine vs taper vs aircraft
Four standard length classes cover the straight-shank world, and everything else is a variation. Screw-machine length (also sold as stub) is the shortest: less flute and less overall length than jobber, so more rigidity and less breakage, at the cost of hole depth [1] [7]. Jobber is the standard general-purpose length [1] [5]. Taper length runs longer than jobber for the same diameter, with a Morse-taper shank version continuing the range to much larger diameters [6] [8]. Aircraft length (long series) is the extended-reach class, from riveted aluminum airframes, sold in fixed lengths such as 6, 8, 12, and 18 in rather than jobber's diameter-proportional lengths [1] [8].
| Class | Diameter | Overall length | Flute length | Character | Sources |
|---|---|---|---|---|---|
| Screw machine (stub) | 1/16 in | 1-5/8 | 5/8 | most rigid | [6] [7] |
| 1/8 in | 1-7/8 | 7/8 | [6] [7] | ||
| 1/4 in | 2-1/2 | 1-3/8 | [6] [7] | ||
| 3/8 in | 3-1/8 | 1-13/16 | [6] [7] | ||
| 1/2 in | 3-3/4 | 2-1/4 | [6] [7] | ||
| Jobber (standard) | 1/16 in | 1-7/8 | 7/8 | general purpose | [5] [6] |
| 1/8 in | 2-3/4 | 1-5/8 | [5] [6] | ||
| 1/4 in | 4 | 2-3/4 | [5] [6] | ||
| 3/8 in | 5 | 3-5/8 | [5] [6] | ||
| 1/2 in | 6 | 4-1/2 | [5] [6] | ||
| Taper length | 1/16 in | 3 | 1-3/4 | longer reach | [6] [8] |
| 1/8 in | 5-1/8 | 2-3/4 | [6] [8] | ||
| 1/4 in | 6-1/8 | 3-3/4 | [6] [8] | ||
| 3/8 in | 6-3/4 | 4-1/4 | [6] [8] | ||
| 1/2 in | 7-3/4 | 4-3/4 | [6] [8] | ||
| Aircraft / long series | 1/16 in | fixed lengths, e.g. 6 in | varies by length offered | maximum reach | [1] [8] |
| 1/8 in and larger | 6, 8, 12, or 18 | varies | [1] [8] |
Screw-machine, jobber, and taper rows are the ANSI B94.11M series values as published independently by ToolNotes (drill bit length chart) and DrillsandCutters (jobber, screw machine stub, and taper length charts); the two agree value for value at every diameter shown. Aircraft-length bits are not on a diameter-proportional series: they are sold in fixed overall lengths, which is why that block carries length classes rather than one number per diameter.
How to choose among them follows from one physical fact: a shorter drill is a stiffer drill. Screw-machine bits exist because shorter flute length and overall length give a more rigid bit that reduces deflection and breakage [1] [7], which is why they live in screw machines, turret lathes, and tight-clearance setups, and why they are rarely seen in retail hardware stores [1]. Jobber is the default for handheld and press work in wood, plastic, and mild metal. Taper and aircraft lengths buy reach at the price of the same rigidity, so they are chosen only when the hole is deep or something is in the way [1] [8].
Jobber drill bit size chart: 1/16 to 1/2 in
The table below is the ANSI B94.11M fractional jobber series for the common 1/16 through 1/2 in range, in the 1/32-and-finer steps that standard sets actually carry. Diameter is given in inches and millimeters, then the two numbers that define jobber length at that diameter: overall length and flute length. Every row was checked against two independent published tables (ToolNotes and DrillsandCutters) and the two agree value for value across the whole range; mm conversions of the diameter are exact (1 in equals 25.4 mm) [5] [6].
| Diameter (in) | Diameter (mm) | Overall length (in) | Flute length (in) | Sources |
|---|---|---|---|---|
| 1/16 | 1.59 | 1-7/8 | 7/8 | [5] [6] |
| 5/64 | 1.98 | 2 | 1 | [5] [6] |
| 3/32 | 2.38 | 2-1/4 | 1-1/4 | [5] [6] |
| 7/64 | 2.78 | 2-5/8 | 1-1/2 | [5] [6] |
| 1/8 | 3.18 | 2-3/4 | 1-5/8 | [5] [6] |
| 9/64 | 3.57 | 2-7/8 | 1-3/4 | [5] [6] |
| 5/32 | 3.97 | 3-1/8 | 2 | [5] [6] |
| 11/64 | 4.37 | 3-1/4 | 2-1/8 | [5] [6] |
| 3/16 | 4.76 | 3-1/2 | 2-5/16 | [5] [6] |
| 13/64 | 5.16 | 3-5/8 | 2-7/16 | [5] [6] |
| 7/32 | 5.56 | 3-3/4 | 2-1/2 | [5] [6] |
| 15/64 | 5.95 | 3-7/8 | 2-5/8 | [5] [6] |
| 1/4 | 6.35 | 4 | 2-3/4 | [5] [6] |
| 17/64 | 6.75 | 4-1/8 | 2-7/8 | [5] [6] |
| 9/32 | 7.14 | 4-1/4 | 2-15/16 | [5] [6] |
| 19/64 | 7.54 | 4-3/8 | 3-1/16 | [5] [6] |
| 5/16 | 7.94 | 4-1/2 | 3-3/16 | [5] [6] |
| 21/64 | 8.33 | 4-5/8 | 3-5/16 | [5] [6] |
| 11/32 | 8.73 | 4-3/4 | 3-7/16 | [5] [6] |
| 23/64 | 9.13 | 4-7/8 | 3-1/2 | [5] [6] |
| 3/8 | 9.53 | 5 | 3-5/8 | [5] [6] |
| 25/64 | 9.92 | 5-1/8 | 3-3/4 | [5] [6] |
| 13/32 | 10.32 | 5-1/4 | 3-7/8 | [5] [6] |
| 27/64 | 10.72 | 5-3/8 | 3-15/16 | [5] [6] |
| 7/16 | 11.11 | 5-1/2 | 4-1/16 | [5] [6] |
| 29/64 | 11.51 | 5-5/8 | 4-3/16 | [5] [6] |
| 15/32 | 11.91 | 5-3/4 | 4-5/16 | [5] [6] |
| 31/64 | 12.30 | 5-7/8 | 4-3/8 | [5] [6] |
| 1/2 | 12.70 | 6 | 4-1/2 | [5] [6] |
Read the table with two habits in mind. Jobber lengths are nominal: they are the standard series, but individual manufacturers round differently, so a listed 3/16 in bit can arrive a few thousandths long or short of 3-1/2 in overall; the series is what sets expectations. And the usable hole depth is bounded by flute length, not overall length, because the flutes must clear chips: the 9 to 14 times diameter rule is the working estimate [1] [2]. Beyond 1/2 in, straight-shank jobber bits continue to 1 in in 1/64 steps under the same standard [4] [5]; larger diameters move to reduced-shank and taper-shank drills. For number and letter gauge diameters (the #1 to #80 and A to Z series that fill the gaps between these fractions), the decimal equivalents live in the tap drill chart's gauge section and in Wikipedia's drill bit sizes reference; we deliberately do not duplicate that chart here [1] [4].
Buying a jobber set: what the chart means at the store
A standard fractional index runs 1/16 to 1/2 in, and the chart above is effectively the table of contents of that index. Three practical notes apply. First, sets sold as 29-piece typically step by 1/64 in across the whole range, which is the same series ANSI B94.11M defines for jobber-length straight-shank twist drills [4] [5]. Second, material and coating change with the length class staying fixed: the same jobber geometry comes in plain HSS, titanium coating, black oxide, cobalt, and carbide, and those choices are covered in our drill bits by material and drill bit coatings guides [5]. Third, check your chuck before the big sizes: a 1/2 in shank needs a 1/2 in (13 mm) chuck, and the drill chuck size chart explains that boundary.
Depth planning is where the flute-length column earns its place. Drilling to a depth near the flute length means periodic withdrawal to clear chips, especially in metal; and when a hole is deeper than the flute allows, that is the signal to move up to a taper-length or aircraft bit rather than to force the jobber [1] [8]. For the drilling itself, speeds by diameter are in the drill speed chart, and pilot-hole sizing for screws is in the pilot hole chart.
Related
For choosing bit material and coating: drill bits by material. For the holes screws tap into: pilot hole chart and tap drill chart. For the shank side of fit: drill chuck sizes. For masonry drills with their own length logic: SDS bit sizes. For spindle speeds by diameter: drill speed chart.
Sources
- Wikipedia, Drill bit sizes: jobber-length 9 to 14 times diameter flute rule with worked examples, screw-machine and aircraft length definitions, ANSI B94.11M scope for jobber straight-shank drills (en.wikipedia.org/wiki/Drill_bit_sizes)
- Albany County Fasteners, Jobber vs Mechanics Drill Bits: 8-12x / 9-14x flute multiple, mechanics length as shorter and more breakage-resistant, fractional increment ranges (albanycountyfasteners.com/blog/jobber-vs-mechanics-drill-bits/)
- Tanner Resources, What is a Jobber Drill: jobber etymology (wholesale distributor, 1850-1950 trade usage), medium length for a wide variety of jobs, 1/2 in drills 4-1/2 in deep (resources.tannerbolt.com/articles-what-is-a-jobber-drill/)
- Wikipedia, Drill bit sizes (fractional section) and Amesweb, straight-shank twist drill standards: ANSI B94.11M fractional jobber series 1/64 to 1 in by 1/64 (en.wikipedia.org/wiki/Drill_bit_sizes; amesweb.info/Tooling/StraightShankScrewMachineLengthTwistDrills.aspx)
- DrillsandCutters, Jobber Length Drill Bit Chart: fractional, letter, and wire sizes with flute and overall lengths per diameter (drillsandcutters.com/jobber-length-drill-bit-chart/)
- ToolNotes, Drill Bit Length Chart: screw-machine, jobber, and taper overall and flute lengths per diameter, ANSI B94.11M derived (toolnotes.com/tooling-and-machining-data/drill-bit-length-chart/)
- DrillsandCutters, Screw Machine (Stub) Drill Bit Chart: stub-series flute and overall lengths per diameter (drillsandcutters.com/screw-machine-stub-drill-bit-chart/)
- DrillsandCutters, Taper Length Drill Bit Chart: taper-series flute and overall lengths per diameter, general-purpose-longer-than-jobber positioning (drillsandcutters.com/taper-length-drill-bit-chart/)