Technical Foundation
What Is a Jobber-Length Drill Bit?
A jobber-length drill bit is the standard, general-purpose twist drill proportion, with an overall length-to-diameter ratio of roughly 12–16× the bit's diameter per the ANSI/ASME B94.11M twist drill standard. That places it between short, rigid stub-length bits (used where extra stiffness or clearance matters more than reach) and long taper-length bits (used for deep holes a jobber bit's flute length can't reach). Jobber length is the default stocked length in most shops because it balances reach and rigidity for the majority of through-hole drilling work.
The point geometry and material determine how the bit performs in a given material. A 118° point is the standard general-purpose angle for mild steel, aluminum and plastics, while a 135° split point adds a self-centering chisel edge that resists walking on start-up and requires less feed pressure, particularly on hard or curved surfaces. On the material side, standard HSS (high-speed steel) is economical for general work, while cobalt alloy (M35/M42) tolerates significantly higher cutting temperatures before it softens, letting it hold an edge in stainless steel and other hard, heat-generating alloys where standard HSS dulls quickly.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Length Ratio | ~12–16× diameter (ANSI/ASME B94.11M) | Defines "jobber" vs. stub or taper-length — sets reach and rigidity trade-off |
| Point Angle | 118° standard, 135° split point | 135° resists walking and needs less starting pressure on hard/curved surfaces |
| Material | HSS vs. cobalt (M35/M42) | Cobalt withstands higher cutting temperatures, holding an edge in stainless and hard alloys |
| Finish/Coating | Bright, black oxide, titanium nitride | Coatings reduce friction and built-up edge, extending tool life independent of base alloy |
| Shank Type | Straight (round) shank, standard chuck fit | Determines compatibility with drill chucks — jobber bits are almost always straight-shank |
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Applications
Where Jobber Length Drill Bits Get Used
Material hardness decides alloy and point geometry more than the hole size does.
General Metal Fabrication
Standard HSS jobber bits with a 118° point handle routine through-hole drilling in mild steel, aluminum and sheet stock on the shop floor.
MRO & On-Site Maintenance
The general-purpose length and 12–16× diameter reach make jobber bits the default carried in maintenance kits for field repairs and equipment servicing.
Sheet Metal & HVAC Ductwork
Split-point 135° jobber bits reduce walking when starting holes on curved or thin-gauge duct and enclosure panels.
Automotive Repair
Cobalt jobber bits hold an edge through hardened fasteners and rusted bolts without the rapid dulling standard HSS would see.
Construction & Structural Steel
Field drilling of structural steel connections relies on jobber-length reach with enough rigidity to avoid bit deflection.
Machine Shop Production Drilling
Cobalt or coated jobber bits sustain cutting speed and hole tolerance across repetitive drilling runs on a mill or drill press.
Woodworking Pilot Holes
Standard HSS jobber bits sized for pilot holes ahead of screws, sized to the fastener's minor diameter to prevent splitting.
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FAQ
Jobber Length Drill Bits Questions, Answered
Jobber, stub, or taper-length — how do I choose?
Jobber length (roughly 12–16× the diameter, per ANSI/ASME B94.11M) is the general-purpose default for through-hole drilling. Stub length is shorter and stiffer, useful when you need extra rigidity or are drilling in a tight space; taper-length drills are longer for reaching deep holes where a jobber bit would run out of flute length.
HSS or cobalt — which should I choose?
Standard HSS handles mild steel, aluminum and general-purpose materials economically. Cobalt (M35/M42) alloy withstands significantly higher cutting temperatures before it softens, so it holds an edge longer in stainless steel, titanium and other hard, heat-generating alloys — at a higher price point.
118° point or 135° split point — what's the difference?
A 118° point is the standard general-purpose angle, ground for typical steel, aluminum and plastic. A 135° split point has a self-centering chisel edge that resists walking on startup, especially on hard, curved or work-hardened surfaces, and needs less starting pressure.
What speed and feed should I run for a given diameter?
Surface speed should drop as diameter increases to hold a constant cutting speed at the edge, and feed rate should increase roughly in proportion to diameter for chip load. Running a small-diameter bit at the same RPM as a large one overheats the edge; running a large bit too fast burns it out quickly.
What causes a jobber bit to walk or wear out prematurely?
Walking is usually a chisel-edge or point-angle mismatch to the surface — a center punch or a 135° split point corrects it. Premature wear typically comes from running too fast for the material and alloy, insufficient coolant/cutting fluid, or using standard HSS on an alloy hot and hard enough to need cobalt.
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