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Irwin Tools IRWIN Step Drill Bit, 3/16-Inch to 7/8-Inch, 3/8-Inch Shank (10234)
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Return this item for free
We offer easy, convenient returns with at least one free return option: no shipping charges. All returns must comply with our returns policy.
Learn more about free returns.- Go to your orders and start the return
- Select your preferred free shipping option
- Drop off and leave!
Purchase options and add-ons
Material | High Speed Steel (HSS) |
Finish Type | Black Oxide |
Shank Type | 3-Flat |
Brand | IRWIN |
Item dimensions L x W x H | 3 x 1 x 6.2 inches |
About this item
- Save time because you don't need to change drills for different-sized round holes in thin materials. Each drill acts as a pilot for the next size.
- Made from industrial-grade high-speed molybdenum steel heat treated for maximum durability. SpeedPoint tip penetrates faster and prevents walking.
- Ideal for drilling holes into thin materials such as stainless steel, copper, brass, aluminum, plastic and laminates.
- Non-skid tip, no need for center punches. 3-faltted hex shank prevents drill chuck slipping. Drill diameters etched in flute for easy identification.
- Backed by a full lifetime warranty.
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Product details
- Is Discontinued By Manufacturer : No
- Product Dimensions : 3 x 1 x 6.2 inches; 0.01 ounces
- Item model number : 10234
- Department : Unisex-Adult
- Date First Available : April 1, 2004
- Manufacturer : IRWIN
- ASIN : B00004THZ0
- Country of Origin : China
- Best Sellers Rank: #20,251 in Industrial & Scientific (See Top 100 in Industrial & Scientific)
- #36 in Step Drill Bits
- #689 in Drill Bits
- Customer Reviews:
WARNING:
Product Description
Product Description
Irwin 10234 Unibit #4 12-Step High Speed Steel 3/8-inch Step Drill Bit, 1/16-inch Steps (3/16- to 7/8-inch) Save time by eliminating the need to change drills when drilling round holes in thin materials. Each smaller size drill also acts as a pilot for the next size. Made from industrial-grade high-speed molybdenum steel heat treated for maximum durability. Ideal for drilling holes into thin materials such as stainless steel, copper, brass, aluminum, plastic and laminates. SpeedPoint tip penetrates faster than previous Unibits and prevents walking. Non-skid tip does away with the need for center punches; 3-faltted hex shank prevents slipping in drill chuck. Drill diameters etched in flute for easy identification. Backed by a full lifetime warranty.
Amazon.com
The Irwin 10234 UniBit #4 12-Step High Speed Steel Fractional Self-Starting Step Drill has a single-flute cutting edge to give you more control and produce true, round holes. Twelve holes range from 3/16 to 7/8 inches, in 1/16-inch increments. A non-skid tip does away with the need for center punches, while the three flatted shanks prevent slipping in the drill chuck. This drill is made from industrial-grade high-speed molybdenum steel heat treated for maximum durability, and it is ideal for work on thinner materials. The multiple steps mean you don't have to have a toolbox with specific size drill bits, and this drill is backed by a full lifetime warranty.
From the Manufacturer
The #4 UniBit Step Drill has 12 holes--3/16-inch to 7/8-inch hole sizes with increments of 1/16-inch- shank size is 3/8-inch. Each UniBit step drill has an easy-to-sharpen, non-skid tip which eliminates skidding and the need for center punching; the tip gives sure starts even on curved surfaces. The single-fluted cutting edge that you will find on the UniBit step drills helps assure true round holes and allows greater control. They are constructed of industrial grade high speed molybdenum steel and heat treated to assure maximum durability. The UniBit step drill has 3 flatted shanks, which prevents slipping in drill chuck. The multiple steps on each UniBit eliminates the need to maintain a toolbox full of specific size drill bits. Full lifetime warranty--each UniBit step drill is warranted to be free from defects in material and workmanship for the life of the tool, except for damage caused by abuse, misuse, or alteration.
Top Brand: IRWIN
From the manufacturer


For over a century, innovation has been the hallmark of IRWIN TOOLS. Beginning in 1885, with the development of the first IRWIN Auger Bit, and progressing with the introduction of Vise-Grip Locking Tools, SPEEDBOR Flat Bits, MARATHON Saw Blades, QUICK-GRIP Bar Clamps, and UNIBIT Step Drill Bits, IRWIN has been at the forefront of the industry, creating superior tools for the professional tradesman.
IRWIN UNIBIT Step Drill Bit #2, 3/16 inch-1/2 inch (6 Steps)
Perfect Hole-Drilling in Metal
IRWIN UNIBIT Step Drill Bits give you maximum drill control to create clean, burr-free holes in metal perfectly sized every single time. With laser-etched sizes inside the flute, hole sizes are easy to identify to prevent over-drilling.
- SpeedPoint tip for fast starts.
- Single fluting cutting edge drills clean, true holes.
- Crafted of durable, high-speed steel.

Precision Crafted
When you're drilling metal, there's no room for error. That's why UNIBIT step drill bits have been designed to deliver clean and accurate holes every time to get the job done right. Precise drilling has never been easier.
Laser-Etched Sizes
Sizes are laser etched into the metal so that they will not wear off even after repeated use.
Clean, Precise Drilling
The SpeedPoint tip is guaranteed to start fast while the single flute design delivers holes that are drilled cleanly and precisely in a variety of materials including mild steel, acrylic glass, laminate, and more.
Step Drills for Every Application
For every trade, application, and material, IRWIN provides the long-lasting accuracy and durability you need.
What's in the box
Customer reviews
Customer Reviews, including Product Star Ratings help customers to learn more about the product and decide whether it is the right product for them.
To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyzed reviews to verify trustworthiness.
Learn more how customers reviews work on AmazonCustomers say
Customers find the drill bit works well for its intended purpose, with a razor-sharp cutting edge that maintains sharpness for at least 40 holes. They appreciate its durability, with one customer noting it lasted through a dozen holes, and its accuracy in creating perfect holes, particularly in stainless steel. Customers praise its value for money, quick operation, and suitability for tight spaces, with one mentioning it's great for drilling out guitar pickup endjacks.
AI Generated from the text of customer reviews
Customers find that the drill bit works well for its intended purpose, with one customer specifically noting its effectiveness on thin metals.
"...I have used the Unibit for this exact purpose, and it worked beautifully, with no damage to the guitar...." Read more
"...This half size bit did the trick beautifully. It’s very sharp and the hole came out very clean. I’m very happy to find this unique bit." Read more
"...Worked perfectly, round hole unlike a typical twist drill bit." Read more
"...I had never installed a pickup before and this 1/2 inch unibit worked perfectly. It will get the job done neatly...." Read more
Customers praise the drill bits' cutting edge, noting they are razor sharp and produce clean cuts, with one customer mentioning they stay sharp for at least 40 holes.
"...This half size bit did the trick beautifully. It’s very sharp and the hole came out very clean. I’m very happy to find this unique bit." Read more
"...This bit was easy to use, sharp, and made a very nice clean hole for my endpin jack install...." Read more
"...It cut smoothly and did not bind up at all. The hole it made was perfectly round and no burs left on the front side...." Read more
"...bit as a result of chipping, this bit held up just fine and still cuts mild steel like it was made of butter...." Read more
Customers find these drill bits durable, with multiple reviews noting their good quality and no signs of damage. One customer mentions they lasted through a dozen holes, while another describes them as well-made for metal work.
"...for this exact purpose, and it worked beautifully, with no damage to the guitar...." Read more
"...A fine guitar is made of fine woods and a fine finish so a drill bit which rips or tears at the finish or even leaves a scratch or rough spot at..." Read more
"...A quick summary: Irwin tools are dependable and are of very good quality...." Read more
"This Irwin step-drill was reasonably priced and has lasted about the longest of any I've had in this size range...." Read more
Customers are satisfied with the drill bits' accuracy, noting that they produce perfect and round holes, with one customer mentioning they work well for reaming out metal holes.
"...On the other hand, this Irwin Unibit could be used to drill a tapered hole, using the strap button screw hole as a pilot hole, followed by the..." Read more
"...Worked perfectly, round hole unlike a typical twist drill bit." Read more
"...It is just the right size to make a hole in metal enclosures for the draw stud of my 1/2" Greenlee manual KO punch, which I will often use to make..." Read more
"...It cut smoothly and did not bind up at all. The hole it made was perfectly round and no burs left on the front side...." Read more
Customers find these drill bits to be good value for money, with one customer noting that the cobalt steel version is worth the extra cost.
"This Irwin step-drill was reasonably priced and has lasted about the longest of any I've had in this size range...." Read more
"...The cobalt steel is worth the extra $$. This is also a GREAT price! Things to keep in mind:..." Read more
"...cuts in clockwise and counterclockwise direction, which means better value for you because you really have two cutting edges...." Read more
"...Irwin Unibits are pretty expensive compared to other brands, but if you want the very best and longevity, definitely get Irwin cobalt bits. ***..." Read more
Customers praise the drill bit's quality, particularly its effectiveness for drilling through thin stock and sheet metal work. One customer mentions it's perfect for guitar pickup endjacks, while another notes it saves time compared to regular bits.
"...This is a must have tool in a guitar workshop." Read more
"This easily drills sheet metal and angle iron the steps make it convenient, not having to change out drillbits...." Read more
"...Great drill bit and very durable. The first one has drilled many many holes in materials often thicker than it was rated for...." Read more
"...It cuts through metal much easier than the traditional drill bits and its so easy to step up the size of the hole...." Read more
Customers appreciate the drill bits' speed, with one customer noting they start easily with or without a pilot hole.
"Irwin has always been a great Step Drill when used as it should be with sheet metal...." Read more
"...Presto...a clean wonderful hole was drilled quickly. I am now a true believer in step bits. This bit also kept its edge very well...." Read more
"...its heavy shank won't fit on an impact drill, and its not hard enough to drill a mower blade (hardened steel)...." Read more
"...I have found them to be the fastest way of drilling thin walled metal (< 4 mm) round and square pipe on site, and they leave a clean circular..." Read more
Customers appreciate the drill bits' size, noting they are perfect for tight spaces and easy to step up, with one customer mentioning they contain all common sizes they need.
"...It cuts quickly and precisely. The holes it produces are smooth with crisp edges." Read more
"...metal much easier than the traditional drill bits and its so easy to step up the size of the hole...." Read more
"Contains all common size I need and the cutting edge is sharp. I bought this to make a hole for gasoline can vent cap...." Read more
"...base and end block, leaving a 1/2" hole that is slightly oversized for most endpin jacks, but completely usable...." Read more
Reviews with images

High Quality Bit, Works well in Plastic, Metal, Wood
Top reviews from the United States
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- Reviewed in the United States on May 24, 2025Size: #4 (3/16-7/8")Style: High Speed SteelVerified PurchaseRecommend
- Reviewed in the United States on June 8, 2015Size: #1 (1/8-1/2")Style: CobaltVerified PurchaseI bought this bit as part of my tool kit to drill endpin jack holes in expensive guitars to mount the endpin jacks for internal pickups. Any drill bit will make a hole, but I wanted to make sure the wood on the guitars would be in perfect condition after the hole was drilled. Causing serious damage to a $5,000 guitar can ruin a guy's day, especially if he's the owner of the guitar. Typically, if no prior hole exists, a new 1/4" hole is drilled with a sharp brad point drill bit, followed by a precision tapered reamer from a guitar luthier supply house. However, sometimes a smaller hole already exists where a strap button was screwed in or a tapered end pin was press fit into a tapered hole. Perhaps the tapered endpin was even glued into the tapered hole and can't be removed without drilling. If a strap button had been screwed in, then the screw hole could be filled and a new hole could be drilled as if none had ever existed, followed by the precision reamer to safely bring the hole to its final dimension. On the other hand, this Irwin Unibit could be used to drill a tapered hole, using the strap button screw hole as a pilot hole, followed by the precision reamer to bring the hole to its final dimension. I have used the Unibit for this exact purpose, and it worked beautifully, with no damage to the guitar. If a tapered wooden strap button has been glued in, the button can be carefully sawed off near its base, and the hole can be drilled with a brad point bit and then reamed, just like the situation where no hole ever existed. But no sawing is needed if a punch is used in the center of the wooden end pin, a 1/8" pilot hole is drilled with a normal twist metal bit or a brad point bit, and the the Unibit is used to drill through the strap button and into the guitar. Eventually, as the Unibit goes deeper, a tapered hole is formed that is larger than the strap button, and the button is drilled completely away, leaving only a nicely tapered hole for the precision reamer to follow and finish to final dimension.
The Unibit can be used after drilling a pilot hole, without using the precision reamer. If that is done, it is best to stop drilling with the Unibit when it reaches the 15/32" step and then finish the hole with a standard 15/32" metal twist bit that will tend to self-center. Or, the Unibit can be used to fully penetrate the guitar base and end block, leaving a 1/2" hole that is slightly oversized for most endpin jacks, but completely usable. Alternatively, buy the 12mm Unibit, which is 15/32", and the hole will be exactly the right size. The precision reamer from the well-known guitar luthier supply house is strongly recommended, but even just the Unibit will safely do a good job. Do put blue painter's tape where the hole will be drilled to help protect the wood from damage. DON'T use the cheap tapered hand reamers, including the one from Irwin -- they do not make good, concentric holes in wood. I've tried -- and failed miserably. The cobalt Unibit is not necessary. The standard (less expensive) tool steel works well, just not as long as the cobalt. For $10 more, the cobalt seems to be the better deal if it is used often.
This is a must have tool in a guitar workshop.
- Reviewed in the United States on December 8, 2024Size: #20 (9/16-1")Style: High Speed SteelVerified PurchaseI had to drill 7/8” hole in 1 1/4” tubing on one side only, and so, I couldn’t use full size step drill bit for being too long. This half size bit did the trick beautifully. It’s very sharp and the hole came out very clean. I’m very happy to find this unique bit.
- Reviewed in the United States on January 23, 2025Size: #20 (9/16-1")Style: High Speed SteelVerified PurchaseNeeded fo a project to enlarge a mounting hole for an axle on a lawn trailer. Worked perfectly, round hole unlike a typical twist drill bit.
- Reviewed in the United States on April 11, 2025Size: #4 (3/16-7/8")Style: High Speed SteelVerified PurchaseIt works
- Reviewed in the United States on May 30, 2022Size: #10 (1/2")Style: High Speed SteelVerified PurchaseI bought this after looking at countless drill bits to find the best one for drilling out the endjack for guitar pickup install. It is a high end $3000. guitar so if I am taking a drill to it i any way, shape, or form, it needed to be the best. A fine guitar is made of fine woods and a fine finish so a drill bit which rips or tears at the finish or even leaves a scratch or rough spot at all is a deal breaker. This bit was easy to use, sharp, and made a very nice clean hole for my endpin jack install. I don't typically write reviews but wanted to write one for this bit for the benefit of other guitarists that are looking for the right drill bit for installing endpin jack for their pickup. The pickup I installed was a K&K pure mini and the guitar is my Martin CEO-7. I had never installed a pickup before and this 1/2 inch unibit worked perfectly. It will get the job done neatly. Of course, make sure you also use blue painters tape on any guitar to protect during drilling.
- Reviewed in the United States on October 26, 2024Size: #4 (3/16-7/8")Style: CobaltVerified Purchasecuts through plastic like butter literally. Hopefully the coating will make it last as long as I live.
- Reviewed in the United States on August 23, 2024Size: #4 (3/16-7/8")Style: High Speed SteelVerified PurchaseIrwin has always been a great Step Drill when used as it should be with sheet metal. I have used this brand for years when I was building street rods.
Top reviews from other countries
- Nick D.Reviewed in Canada on November 27, 2017
5.0 out of 5 stars Cuts like a hot knife through butter!
Size: #3 (1/4-3/4")Style: High Speed SteelVerified PurchaseCuts like a hot knife through butter!
- PietroReviewed in Canada on April 28, 2015
5.0 out of 5 stars works great!
Size: #2 (3/16-1/2")Style: CobaltVerified PurchasePowerfull
- L-AReviewed in Canada on July 14, 2024
5.0 out of 5 stars Great deal
Size: #3 (1/4-3/4")Style: CobaltVerified PurchaseHappy with product, great deal , well built,thanks
- Burke KilgourReviewed in Canada on December 28, 2023
5.0 out of 5 stars Just what i wanted
Size: #20 (9/16-1")Style: High Speed SteelVerified PurchaseFactory sealed never opened exactly what I needed
- GilReviewed in Canada on January 20, 2018
5.0 out of 5 stars Five Stars
Size: #1 (1/8-1/2")Style: CobaltVerified PurchaseA very good quality tool.