The best hole saw size for 1 1/4 EMT is 1.655 inches or 1 5/8 inches, depending on the required fit. This size allows the 1 1/4 inch conduit hole size to pass through materials like electrical boxes or enclosures cleanly.
This article will help you choose the right tool for making clean holes for your electrical work. Working with electrical conduit requires precision. Getting the hole size wrong can make installation hard or even unsafe. We focus here on 1 1/4 EMT, a common size for many electrical jobs.
Why Hole Size Matters for 1 1/4 EMT
EMT stands for Electrical Metallic Tubing. It is a lightweight, unthreaded metal pipe. Electricians use it to protect wires. Proper sizing when drilling holes is key. If the hole is too small, the conduit will not fit. If the hole is too large, the conduit might not be secure. This can create hazards.
The outside diameter (OD) of 1 1/4 EMT is what really matters. This measurement dictates the conduit fitting hole diameter you need to create.
Trade Size vs. Actual Diameter
Conduit sizes, like 1 1/4, are called “trade sizes.” These names are historical. They do not always match the actual physical measurements. For 1 1/4 EMT:
- Trade Size: 1 1/4 inches
- Actual Outside Diameter (OD): 1.660 inches
When you are drilling hole for 1 1/4 conduit, you must aim for a size close to the OD.
Choosing the Right Hole Saw for 1 1/4 EMT
When looking for a hole saw for 1.25 inch EMT, you have a few options. The goal is usually a snug fit.
Option 1: The Exact Fit
Some manufacturers make specialized bits. These bits aim for the exact OD of the conduit.
- Required Diameter: 1.660 inches
Finding a standard hole saw in exactly 1.660 inches can be hard. Often, you look at the closest metric or imperial size available.
Option 2: The Common Oversize (The Standard Go-To)
Many electricians use a standard size that is slightly larger. This accounts for minor variations in the conduit or the material being drilled.
- Common Hole Saw Size Used: 1 5/8 inches (or 1.625 inches)
Wait, 1 5/8 inches is slightly smaller than 1.660 inches! Why use it?
Sometimes, you are working with older EMT or slightly thinner wall material. Also, you might be passing the EMT through drywall or wood where a very tight fit is not required, but ease of insertion is preferred. However, for securing the conduit, a slightly larger hole can cause issues if you rely on conduit clamps that fit snugly around the pipe.
Option 3: The Best Fit for Knockouts and Panel Entry
When dealing with electrical box knockout size or installing conduit through the wall of a metal enclosure, you often need a size that matches standard knockout punches.
- Standard 1 1/4 Knockout Size: 1.655 inches
This size (1.655″) is the size an EMT knockout punch size for 1 1/4 trade size will create. If you are using a hole saw to mimic a knockout, this is the ideal target hole diameter for trade size 1 1/4 conduit.
| Trade Size | Actual OD (Inches) | Ideal Hole Saw Size (Inches) | Standard Knockout Size (Inches) |
|---|---|---|---|
| 1 1/4 | 1.660 | 1.655 (or 1 21/32) | 1.655 |
Comparing Hole Saw Sizes
To make things easy, let’s look closely at the common options and how they work when installing 1 1/4 EMT through panel walls.
1 1/2 Inch Hole Saw (1.500″)
This is too small. A 1 1/4 EMT pipe (1.660″ OD) will not fit into a 1.500″ hole. Do not use this size.
1 5/8 Inch Hole Saw (1.625″)
This is slightly smaller than the actual OD (1.660″). This can be a very tight fit. It might require significant force to push the EMT through. For soft materials like thin plywood, it might work. For metal enclosures, it could scratch the conduit or the box opening, making future removal difficult.
1 11/16 Inch Hole Saw (1.6875″)
This size is slightly larger than the 1.660″ OD. This gives a loose fit. If you plan to use a locknut or coupling to secure the pipe, this looseness might be fine. If the pipe needs to be perfectly snug against the panel surface, this might be too large.
The Target: 1.655 Inches
For the best, most professional results that match factory knockouts, aim for 1.655 inches. Since 1.655″ is hard to find on a standard hardware store rack, electricians often use a step-drill bit or adjust slightly using a 1 5/8″ hole saw followed by light filing or reaming if needed. If you are cutting sheet metal panels, using a dedicated 1 1/4 EMT knockout punch is faster and guarantees the correct size (1.655″).
Deciphering the Hole Saw Chart for EMT
If you frequently work with different conduit sizes, a quick reference guide is very helpful. This hole saw chart for EMT shows the common trade sizes and their corresponding best hole saw diameters.
| EMT Trade Size | Actual OD (in.) | Recommended Hole Saw Size (in.) | Notes |
|---|---|---|---|
| 1/2″ | 0.706 | 11/16 (0.6875) or 3/4 (0.75) | Tight fit vs. easy fit |
| 3/4″ | 1.050 | 1 1/16 (1.0625) | Close to actual OD |
| 1″ | 1.315 | 1 5/16 (1.3125) | Very close to actual OD |
| 1 1/4″ | 1.660 | 1.655 (Knockout Size) | Target size for professional fit |
| 1 1/2″ | 1.900 | 1 7/8 (1.875) or 2 (2.00) | Varies based on connector type |
| 2″ | 2.375 | 2 3/8 (2.375) | Often matches OD exactly |
Notice how for smaller sizes, the OD and the hole size are very close. For 1 1/4″, the standard knockout size (1.655″) is slightly less than the OD (1.660″). This difference is tiny—less than 0.005 inches—but it’s engineered to allow the EMT to seat properly when a locknut is used.
Steps for Drilling the Perfect Hole
Regardless of the material you are drilling through—drywall, wood, plastic, or metal—the technique matters for a clean result.
1. Material Safety First
Always wear safety glasses. If drilling metal, wear heavy gloves. Ensure the material you are drilling is securely clamped down. Sparks can be dangerous if you drill thick steel.
2. Marking and Centering
Use a permanent marker to mark the exact center point for your drilling hole for 1 1/4 conduit.
- If using a hole saw: Look for the center drill bit that comes with the saw. Start drilling slowly. The center bit guides the main saw teeth.
- If using a knockout punch: Center the knockout die exactly where you marked the hole. Use the provided draw stud to tighten the punch.
3. Selecting the Right Hole Saw Bit
For metal panels, you must use a high-speed steel (HSS) or carbide-tipped hole saw. Standard bi-metal saws work for wood and plastic but dull very quickly on steel.
- Use a high-quality EMT size hole saw that is rated for the material thickness.
4. Drilling Technique
Hole saws work best when you let the tool do the cutting. Do not push too hard.
- Speed: Use a slower RPM for thicker or harder materials (like steel). Faster RPM is fine for wood or plastic.
- Lubrication: When drilling metal (especially thick metal), use cutting oil. Dip the saw teeth in oil or spray oil frequently. This keeps the teeth cool. Cooling prevents premature dulling and gives a cleaner cut.
- Pecking: For thick materials, drill a bit, pull the saw out, clear the shavings (chips), and then continue. This prevents the saw from binding or overheating.
5. Finishing the Hole
After cutting the hole, inspect the edges.
- Metal Edges: Use a metal file, sandpaper, or a rotary tool (like a Dremel) with a grinding bit to smooth any sharp edges. Burrs left on the edge can damage wire insulation when you pull the wires through the conduit later. This is crucial when installing 1 1/4 EMT through panel surfaces where wires will be pulled tight.
- Wood/Plastic Edges: A light sanding often suffices to remove minor plastic fuzz or wood splinters.
Comprehending Knockout Tools vs. Hole Saws
Many installers prefer specialized knockout tools when penetrating metal enclosures like circuit breaker panels or junction boxes.
The Role of the EMT Knockout Punch Size
A knockout punch is designed specifically for electrical box standards. When you use a 1 1/4 trade size knockout punch, it creates a hole exactly sized for the conduit fitting threads to pass through and secure tightly with a locknut.
- Benefit of Punch: Guaranteed precision (1.655 inches). Fast operation on thinner steel.
- Drawback of Punch: Only works on thinner gauge metal (usually up to 10 gauge steel). Requires a large wrench or hydraulic driver for large sizes.
When to Use a Hole Saw
A hole saw is superior when:
- You are drilling through very thick steel where a punch cannot reach or exert enough force.
- You are drilling through materials not intended for knockouts, like thick concrete blocks, heavy wood structures, or thick plastic.
- The material thickness exceeds the capacity of your available knockout set.
If you choose the hole saw route for metal, always use a high-quality, aggressive-tooth saw and cutting fluid to achieve a clean cut near the 1.655″ target.
Fathoming Conduit Fittings and Hole Size
The size of the hole directly affects how you connect the conduit on the other side. This relates directly to the required conduit fitting hole diameter.
Locknuts and Couplings
When 1 1/4 EMT passes through a knockout in an electrical panel, a locknut secures it. The locknut has teeth that grip the outside of the pipe and the inside of the panel.
If your hole is too large (e.g., 2 inches), the teeth of the locknut cannot properly grip the conduit wall. This creates a weak connection. This looseness might also allow moisture or dust into the enclosure.
If your hole is too small (e.g., 1 5/8″ when the OD is 1.660″), the EMT might not fit at all, or you might have to force it, damaging the locknut threads or the conduit itself.
The ideal 1.655″ hole size ensures that when the locknut is tightened, the conduit is firmly seated, meeting safety codes for secure wiring protection.
Bushings
Bushings are installed on the raw edge of the drilled hole, especially in sheet metal, to protect the wire insulation. The internal diameter of the bushing must accommodate the 1.660″ OD of the EMT, while the outer diameter of the bushing must fit snugly into the 1.655″ hole or slightly overlap it to seal the edge. Using the standard knockout size helps maintain compatibility with these standard fittings.
Advanced Considerations for Drilling Different Materials
The best hole saw size remains centered around 1.655″, but the drilling process changes drastically based on the medium.
Drilling Wood or Plywood
Wood is the easiest material. A standard bi-metal hole saw will work great.
- Tip: To prevent tear-out on the backside of the wood, drill about three-quarters of the way through. Then, flip the material over and finish the hole from the back. This prevents the saw teeth from ripping out large chunks as they exit.
Drilling Plastic or PVC Conduit Boxes
If you need to drill a hole in a plastic junction box to accept EMT stub-up, the fit needs to be slightly tighter than metal, as plastic is softer and less forgiving.
- You might opt for a slightly smaller hole saw for 1.25 inch EMT, such as 1.625″ (1 5/8″), to ensure the plastic grips the conduit better. However, verify that the connecting fitting you plan to use will accommodate this slight difference.
Drilling Thick Steel Panels (Enclosures)
This is the toughest job.
- Tool Quality: Use only cobalt or carbide-tipped hole saws.
- Pilot Hole: Always drill a pilot hole first, slightly smaller than the center drill bit of the hole saw. This stabilizes the main saw.
- Coolant: Use heavy-duty cutting fluid or cutting wax. Drilling dry steel will burn out the saw almost instantly and create incredibly sharp burrs.
Reviewing the Need for Precision
The slight discrepancy between the trade size (1 1/4″), the actual diameter (1.660″), and the standard knockout size (1.655″) is important for professional installers.
When you are tasked with an installation requiring compliance with NEC (National Electrical Code) standards for enclosures, the goal is to replicate the factory knockout dimensions. Therefore, the hole diameter for trade size 1 1/4 conduit should be as close to 1.655 inches as possible.
If you are using a non-standard fitting, or simply passing the conduit through a wall where it will be supported by straps later, a small variation (like 1.660″ or even 1.6875″) might be acceptable, but it is always best practice to use the size dictated by the locking hardware.
FAQ: Frequently Asked Questions About 1 1/4 EMT Hole Sizing
What is the actual outside diameter of 1 1/4 EMT conduit?
The actual outside diameter (OD) of standard 1 1/4 inch EMT conduit is 1.660 inches.
What size hole saw should I use for 1 1/4 EMT if I don’t have a knockout punch?
If you do not have a knockout punch, the ideal target size for a clean fit with standard fittings is 1.655 inches. If 1.655″ is unavailable, 1 11/16″ (1.6875″) is often used, though it may result in a slightly looser fit. Avoid sizes smaller than 1.625″.
Is 1 5/8 inch the correct hole saw size for 1 1/4 EMT?
1 5/8 inch (1.625″) is slightly smaller than the conduit’s actual OD (1.660″). While sometimes used for a very tight friction fit, it is generally not the ideal EMT size hole saw because the pipe may not pass through, or it may be too tight for standard couplings. The standard knockout size is 1.655″.
Can I use a drill bit instead of a hole saw for making a hole for 1 1/4 conduit?
A standard drill bit can only create a small starting hole (pilot hole). You cannot drill a 1.655-inch hole with a standard bit unless you use a large step drill bit designed for this purpose. A hole saw is the correct tool for making large, round cuts.
How do I ensure the EMT is secured if the hole is slightly too big?
If your hole ends up slightly oversized, you must rely on the locknuts and bushings being properly tightened. If using straps or clamps on the exterior of the panel, ensure the straps are rated specifically for 1 1/4 EMT to provide the necessary support against movement.
Are there specific rules for drilling holes in metal panels?
Yes. When installing 1 1/4 EMT through panel enclosures, the holes must be clean, free of sharp edges (burrs), and the proper electrical box knockout size must be used to ensure secure fastening with locknuts. Check local electrical codes, but standard practice demands a hole size near 1.655″.