Cast iron asks a lot from a drill bit, especially around sink cutouts, machinery repairs, brackets, and garage projects where heat and hardness can chew through weaker steel fast. You need the right size, the right shank, and a point style that starts cleanly instead of skating across the surface like a stone on ice.
The eight picks below focus on cobalt and HSS options with practical lengths, storage cases, and size ranges that suit both occasional home fixes and more demanding metalwork. You’ll also see where each one fits best, because a 1/8-inch set and a 3/4-inch reduced-shank bit solve very different problems.
Quick Look At The Shortlist
Narwhal 1/8 Inch Cobalt Drill Bits 13 Pack M35
Mudder 30 Pieces 1/8 Drill Bit M35 Cobalt Set
CaRoller 1/8 Inch Cobalt Drill Bit Set 10 Pack
RCINDUS 20PCS 1/8 Cobalt Drill Bit HSS M35
BECOLLO 3/4 Cobalt Drill Bit 1/2 Reduced Shank
LU&MN M35 Jobber Drill Bits 1/2 5 Pcs
WildBossy M35 5% Cobalt Metric Drill Bits Set
KENDO 29PC Drill Bit Set 1/16-1/2 135 Tip HSS
More Details On Our Top Picks
Narwhal keeps the focus tight here, with a 1/8-inch size and M35 cobalt steel aimed at small metal holes that need a clean start. The 135-degree split point helps the bit bite sooner, so it makes sense for thin brackets, cast iron fittings, and other jobs where wandering is annoying.
The 2.55-inch length is compact, which helps in tighter drill setups and leaves less bit hanging out than longer jobber bits. The trade-off is obvious, though, this is a narrow-size pack, so your setup stays specialized rather than flexible.
Positives
- M35 cobalt construction suits hard metal work and holds up better than plain HSS in tough material.
- The 135-degree split point helps the tip start with less skating on cast iron.
- Shorter 2.55-inch length keeps the bit handy in tighter spaces and compact drill setups.
- Thirteen pieces give you a practical reserve for repeat small-diameter tasks.
Points To Note
- Single-size packs are specialized, so they do not cover larger hole sizes.
- Like most small cobalt bits, storage matters because loose bits can nick each other in a toolbox.
Feature Card
Who It Suits Best
You’ll like this most for detailed metalwork, repair jobs, and anyone who repeatedly drills 1/8-inch holes in cast iron or stainless steel.
Where A Sibling Pick Shines
Mudder 30 Pieces 1/8 Drill Bit M35 Cobalt Set suits workshop users better when you want many more 1/8-inch bits on hand for higher turnover.
This Mudder set looks built for high turnover, with thirty 1/8-inch bits ready for the kind of work that burns through small diameters over time. In a busy shop or garage, that kind of reserve can matter more than fancy packaging, especially for cast iron and stainless jobs where bit wear adds up.
The trade-off is simple, you stay locked into one size. That works well for repeat holes, but a mixed project bag will still need another set for larger openings.
What We Like
- Thirty bits suit frequent drilling sessions where small bits tend to disappear or wear down.
- M35 cobalt construction gives the set a stronger fit for harder metals than basic general-purpose bits.
- The single-size format keeps the case easy to sort and quick to grab from a tool drawer.
- It handles more than cast iron, so the set also fits stainless steel, woodwork, and plastic tasks.
Room For Improvement
- Only one diameter is included, so versatility stays limited.
- Without size variety, you may still need another set for pilot holes or larger hardware.
Details At A Glance
Made For
You’ll get the most value from this set in a workshop, maintenance cart, or home tool kit that sees steady 1/8-inch drilling.
Swap It Out When
CaRoller 1/8 Inch Cobalt Drill Bit Set 10 Pack is the better fit for you when a smaller reserve and a storage case matter more than sheer quantity.
CaRoller keeps things tidy with a ten-pack and a storage case, which is helpful when you want your 1/8-inch bits organized instead of loose in a drawer. That makes it a sensible choice for home mechanics and hobby spaces where small parts vanish easily.
Compared with Narwhal’s shorter pack, this one feels more about storage convenience than compact length. The honest read is that a case matters most when your tools travel between shelves, boxes, and job sites.
Upsides
- The included case helps keep small bits sorted and easier to protect from edge damage.
- M35 cobalt and the 135-degree tip suit hard metal work and cleaner starts.
- Ten pieces are enough for a handy reserve without turning storage into clutter.
- The 1/8-inch size works well for pilot holes and light fastening prep.
Softer Spots
- The pack stays size-specific, so it will not replace a wider drill set.
- Storage cases help, but they still need regular use so bits do not end up scattered elsewhere.
Core Details
Whose Shelf It Belongs On
You’re a strong match for this set when you keep a small kit in a garage, service van, or bench drawer and want your 1/8-inch bits easy to find.
A Better Fit Elsewhere
RCINDUS 20PCS 1/8 Cobalt Drill Bit HSS M35 is the smarter choice for you when a larger same-size supply matters more than a case.
RCINDUS sits in that useful middle ground where the set is still compact, but the 20-piece count gives you some breathing room. For home repairs that move between cast iron, steel, wood, and plastic, that kind of mixed-material reach keeps the toolbox simpler.
It is not the most specialized option here, and that is part of the appeal. You get a broad-use bit set without jumping to a larger metric spread or a heavy-duty reduced-shank design.
Bright Spots
- Twenty bits give you a sensible reserve for repeated 1/8-inch drilling.
- The multi-material focus covers more than cast iron, which helps in mixed repair work.
- M35 cobalt construction is a better fit for harder stock than plain steel bits.
- The set size is manageable for a bench drawer or mobile tool bag.
Worth Noting
- The single size keeps it from replacing a broader assortment of diameters.
- General-purpose sets can be handy, but they are not as tailored as a dedicated hard-metal pack.
Technical Sheet
Right Fit For
You’ll appreciate this set most in a general-purpose workshop where cast iron is only one part of a larger mix of repair tasks.
Look Elsewhere When
WildBossy M35 5% Cobalt Metric Drill Bits Set fits you better when your projects lean on metric sizing rather than 1/8-inch imperial bits.
Once you move into 3/4-inch holes, the conversation changes a lot, and this BECOLLO bit is aimed squarely at that heavier work. The 1/2-inch reduced shank with three flats helps the bit stay seated in larger chucks, which matters on stronger drills used for thick cast iron or hard steel.
You only get two pieces, so this is not about building a wall of extras. It’s a focused choice for larger openings, and that focus is exactly what many repair and fabrication tasks need.
Strong Points
- The 3/4-inch cutting size suits large-hole work in hard metal.
- The reduced 1/2-inch shank improves compatibility with many standard drill chucks.
- Three flats help limit slippage during tougher drilling sessions.
- Two-piece packaging gives you a backup bit without unnecessary bulk.
Areas To Watch
- Large bits ask a lot from the drill, so a weaker tool may feel underpowered.
- The set is purpose-built, so it is not useful for smaller pilot-hole work.
- Storage matters here, because large cobalt bits can take up more space in a drawer.
Feature Rundown
The Right Fit
You’ll get the most from this bit on fabrication jobs, equipment repair, or any project where a wide hole in cast iron is part of the plan.
Another Choice May Suit
LU&MN M35 Jobber Drill Bits 1/2 5 Pcs works better for you when you want heavy metal capability but need a smaller 1/2-inch cutting size.
LU&MN targets the heavier end of the drilling range with 1/2-inch jobber bits, and that makes sense for thick stock, cast iron, and other demanding metal jobs. The 135-degree split point is a useful detail here because large bits need a steady start, not a wandering one.
The five-piece count keeps the set lean, which suits a serious tool drawer better than a cluttered catch-all box. You may find it especially sensible in a shop that values fewer, larger bits over a giant mixed kit.
Best Bits
- 1/2-inch size fits larger holes in heavy metal and cast iron.
- M35 cobalt HSS brings a harder-working feel for demanding materials.
- The 135-degree split point helps control the start on tough surfaces.
- Straight shank keeps the design straightforward for standard drill setups.
- Five pieces give you backups without filling the case with extras you may not use.
Softer Spots
- The set is size-specific, so it won’t help with small pilot holes.
- Large bits can be harder to store neatly if your tool space is tight.
At A Glance
Best Suited To
You’re in the sweet spot for this set when your projects involve larger holes in thick cast iron or similarly hard metal.
Where A Sibling Pick Shines
BECOLLO 3/4 Cobalt Drill Bit 1/2 Reduced Shank is the better fit for you when you need a wider diameter and a reduced shank for more machine compatibility.
WildBossy takes the metric route, and that matters a lot in shops that live on millimeters instead of fractions. A 1mm to 10mm spread gives you a useful ladder of sizes for hardware, sheet metal, and cast iron projects that need more than one hole diameter.
Compared with the single-size sets earlier in the list, this one gives you real flexibility. The trade-off is that the pieces are smaller than the heavy-duty options, so it suits detail work more than large openings.
Highlights
- The 1mm to 10mm range covers a broad span of metric drilling needs.
- Nineteen pieces make it easier to match hole size to the job.
- 5% cobalt content is a strong fit for harder metal work.
- Straight shank jobber length bits are familiar and easy to sort in a kit.
Minor Gripes
- Metric sizing is great for some shops, but not as handy for every imperial setup.
- Smaller diameter bits still need careful storage so tips do not get nicked together.
Feature Snapshot
Who Should Grab It
You’re a good match for this set if your projects lean metric and you want one kit for a spread of hole sizes in metal.
Skip It When
KENDO 29PC Drill Bit Set 1/16-1/2 135 Tip HSS fits you better when you want a wider imperial range with a handy storage case.
KENDO rounds out the list with a size spread that reaches from 1/16 inch up to 1/2 inch, which gives you a lot of day-to-day flexibility. The black and gold finish adds a cleaner visual distinction in the case, and that can help when you’re moving quickly between sizes on a busy bench.
For mixed material work, this one sits comfortably between the very focused small-size sets and the heavier single-bit options. You may still want a dedicated large-diameter bit for thick cast iron, but for general drilling it covers plenty of ground.
Plus Points
- The 29-piece range gives you many sizes without splitting into multiple sets.
- 1/16-inch to 1/2-inch coverage helps with pilot holes and mid-size openings.
- 135-degree tips support cleaner starts on harder surfaces.
- The storage case keeps the set more portable and easier to sort.
Small Caveats
- Broad range sets can be handy, but they may not feel as specialized as a dedicated cobalt pack.
- Black and gold finishes help identification, yet careful storage still matters to protect the cutting edges.
Core Details
Built With In Mind
You’ll like this set most in a home shop or maintenance space where you want one drill kit that covers many common hole sizes.
Where Another Pick Suits Better
Narwhal 1/8 Inch Cobalt Drill Bits 13 Pack M35 is the smarter fit for you when your work stays focused on small, repeat 1/8-inch holes in cast iron.
How To Choose The Right Drill Bits For Cast Iron
Start With The Material Mix
Cobalt bits, especially M35 and 5% cobalt versions, make sense because cast iron is hard enough to punish softer steel quickly. The cobalt content helps the edge stay useful longer in demanding metal, though you still need steady feed pressure and a drill that can hold a stable speed.
Plain HSS bits can work for lighter jobs, but they are better suited to occasional use or softer stock. For regular cast iron work, the stronger material is usually the safer long-term choice for your toolkit.
Match The Size To The Job
Small 1/8-inch bits are great for pilot holes, anchors, and careful starts, while 1/2-inch and 3/4-inch bits handle larger openings. That size gap matters more than many shoppers expect, because a drill bit can be excellent and still be the wrong shape for the hole you need.
Mixed-size sets help with general use, but single-size packs are often smarter when you repeatedly drill the same diameter. The cleanest setup is the one that matches your actual workbench routine, not the one with the biggest count.
Pay Attention To Point Shape And Shank Design
A 135-degree split point helps the bit bite sooner and reduces wandering on slick surfaces, which is useful on cast iron and other hard metal. Reduced shanks, like 1/2-inch shanks on larger bits, improve compatibility with common chucks and help the tool stay secure under load.
Those details sound small, but they change how the bit feels in use. A well-matched point and shank can make the first few seconds of drilling calmer and more controlled.
Think About Storage And Frequency
Case included sets suit garage shelves and mobile kits, because small bits are easy to lose. Heavy-use shops often do better with larger counts of a single size, while occasional home projects usually benefit from a broader set with better organization.
Maintenance stays simple, wipe bits clean, keep them dry, and store them so cutting edges do not rub together. That bit of care helps more than most people expect, especially once you start drilling harder metal on a regular basis.
Things Worth Knowing First
Wrong Turns To Avoid
A common mistake is choosing a soft, general-purpose bit for cast iron and expecting clean results. Another is buying only one diameter and then discovering the project needs both pilot and finish holes.
Storage gets overlooked too. Loose bits knock against each other, and the edge damage shows up later as rough starts and extra effort at the drill.
The Upgrade Payoff
Higher-tier bits usually cost more because cobalt content, tighter tip design, and larger diameters demand more material and more careful manufacturing. Reduced-shank designs also add function, since they let bigger bits work with more drill chucks.
That extra spend makes sense for regular metalwork, thick cast iron, or anyone who needs fewer interruptions. For occasional household jobs, a simpler set can still be the smarter balance.
Frequently Asked Questions
Are cobalt bits better for cast iron?
Yes, cobalt bits are a strong fit because they handle hard material better than basic steel bits. They still need the right speed and a steady hand.
What size drill bit works for pilot holes in cast iron?
Small sizes like 1/8 inch are common for pilot holes and controlled starts. The right final size depends on the hardware or opening you need.
Do I need a split point for cast iron?
A split point helps reduce wandering when the bit first touches the surface. That matters a lot on hard, smooth metal.
Why do some large drill bits have reduced shanks?
Reduced shanks let larger bits fit more standard drill chucks. They also help the tool stay seated better during heavier drilling.
Should you buy a set or a single-size pack?
A set works well for mixed projects and general repair work. A single-size pack makes more sense when you drill the same diameter over and over.
Closing Thoughts
You do not need the fanciest drill bit set to handle cast iron well, but you do need the right mix of material, point shape, and size. Small cobalt packs suit careful work, larger reduced-shank bits fit heavier holes, and broad sets make life easier in a general shop. Match the bit to the job you actually do, and the rest gets much simpler.
