What an M5 clearance hole is and why it matters
An M5 clearance hole is a drilled opening sized to let an M5 bolt pass through without threading. The bolt slides freely through the hole rather than screwing into it. This is different from a tapped hole, which is threaded to accept the bolt's threads.
Clearance holes are used when you want to fasten two pieces together with a bolt, washer, and nut on the opposite side — or when the bolt needs to move through one part to thread into another. The hole must be large enough that the bolt does not bind or require force to insert, but not so large that the bolt sits loose or tilts.
Getting the size right matters because an undersized hole will jam the bolt, and an oversized hole will let the bolt rattle or misalign. Manufacturers and engineers specify clearance hole sizes in standards so that anyone building or repairing something knows exactly what to drill.
Key Takeaways
- The standard M5 clearance hole diameter is 5.5 mm for normal clearance and 6 mm for loose clearance, depending on how much wiggle room you need.
- Normal clearance (5.5 mm) is the default choice for most assembly work and allows the bolt to slide in smoothly without binding.
- Loose clearance (6 mm) is used when parts need to align before tightening or when the bolt must move slightly during installation.
- Drill bit sizes are labeled in millimeters or fractional inches; a 7/32-inch bit is close to 5.5 mm and works for normal M5 clearance.
- Always measure your bolt diameter and test the fit in scrap material before drilling your final piece.
Standard clearance hole sizes for M5 bolts
The ISO 273 standard and DIN 13 specification define clearance hole sizes for metric bolts. For an M5 bolt, the two most common sizes are:
| Clearance Type | Hole Diameter (mm) | Hole Diameter (inches) | Common Use |
|---|---|---|---|
| Normal | 5.5 | 0.217 | Standard assembly, bolt slides smoothly |
| Loose | 6.0 | 0.236 | Alignment tolerance, parts may shift slightly |
| Close | 5.3 | 0.209 | Precision work, minimal play (rare for M5) |
Normal clearance (5.5 mm) is the default for most work. The bolt passes through without resistance, and the fit is snug enough that the bolt does not rattle once tightened. Loose clearance (6 mm) is chosen when you are assembling parts that need to slide into position before the bolt is tightened, or when manufacturing tolerances are wide and you want to avoid jamming.
Drill bit sizes that match M5 clearance holes
Metric drill bits are labeled in millimeters, so finding the right size is straightforward if you have a metric set. A 5.5 mm bit produces a normal M5 clearance hole, and a 6 mm bit produces a loose clearance hole.
If you are working with fractional inch drill bits (common in older tool sets or in regions that use imperial measurements), the closest sizes are:
- 7/32 inch (0.219 inch or 5.56 mm) — very close to 5.5 mm normal clearance; this is the standard fractional equivalent.
- 15/64 inch (0.234 inch or 5.94 mm) — very close to 6 mm loose clearance.
The 7/32-inch bit is the most common substitute when metric bits are not available. The difference between 5.5 mm and 5.56 mm is small enough that it does not affect fit in normal assembly work. If you are unsure which bit you have, measure the bit itself with calipers or a ruler marked in millimeters.
How to drill an accurate M5 clearance hole
Accuracy starts before the drill touches the material. Mark the hole location with a center punch — a small pointed tool that makes a shallow dent. This dent guides the drill bit and prevents it from wandering across the surface. Without a center punch, the bit can skate sideways and produce a hole in the wrong spot.
Clamp or hold the workpiece firmly so it does not spin or shift when the drill bit engages. A spinning workpiece can jam the bit or throw your hand. If you are drilling metal, use a cutting fluid or light machine oil to reduce friction and heat; this makes the hole cleaner and extends the bit's life. For plastic or wood, no fluid is needed, but drill slowly to avoid melting plastic or splintering wood.
Drill at a moderate speed — not so fast that the bit overheats, not so slow that it binds. For a 5.5 mm bit in steel, a speed around 1000 to 1500 revolutions per minute works well. In aluminum, you can go faster. Stop occasionally to clear chips from the hole. When the bit breaks through the back side, ease off pressure to avoid tearing the exit edge.
After drilling, test the fit with an actual M5 bolt. The bolt should slide through by hand without jamming or requiring a tap with a hammer. If it binds, the hole is too small. If the bolt rattles or tilts, the hole is too large.
Difference between clearance holes and tapped holes
A clearance hole is smooth and unthreaded. The bolt passes through and is held by a nut on the other side, or it threads into a tapped hole in a third piece. A tapped hole has threads cut into it so the bolt can screw directly in without a nut.
For an M5 bolt, a tapped hole is drilled with a smaller bit first (usually 4.2 mm for metric threads), then a tap tool is turned into the hole to cut the threads. This is more work but allows you to fasten parts with a bolt alone, without a nut. Clearance holes are faster and are used when you have access to both sides of the joint or when a nut is acceptable.
The choice depends on your design. If you are fastening a bracket to a wall and cannot reach behind it with a wrench, you need a tapped hole. If you are joining two flat pieces and can access both sides, a clearance hole with a nut is simpler and often stronger.
Common mistakes when drilling M5 clearance holes
The most frequent error is using the wrong bit size — often a bit that is too small, which jams the bolt. This happens when someone confuses the clearance hole size with the bolt's core diameter (the smallest part of the threaded section). An M5 bolt's core is about 3.7 mm, but the clearance hole must be larger than the bolt's outer diameter, which is 5 mm.
Another mistake is drilling without a center punch, which causes the hole to be off-target. A hole that is 2 or 3 mm away from where it should be can prevent parts from aligning. Punching takes seconds and saves the workpiece.
Drilling too fast in metal can overheat the bit and dull it quickly, or cause the bit to grab and twist the workpiece. Drilling too slowly in plastic can melt the material and clog the hole with softened plastic. Finding a moderate speed and stopping to clear chips prevents both problems.
When to use normal versus loose clearance
Use normal clearance (5.5 mm) for most assembly work. It is the standard choice, and it balances a snug fit with ease of insertion. The bolt will not rattle once tightened, and you do not need extra space for alignment.
Use loose clearance (6 mm) when parts must slide or shift before tightening. This is common in machinery where one part must align with another before the bolt is tightened, or in situations where manufacturing tolerances are loose and you want to avoid jamming. Loose clearance also helps when you are using a bolt with a large washer that might interfere with a tight hole.
Close clearance (5.3 mm) is rarely used for M5 bolts in general work. It is specified for precision applications where minimal play is required, but it is harder to achieve and offers little practical benefit in most assembly tasks.
Frequently Asked Questions
Can I use a 6 mm bit for all M5 clearance holes?
You can, but it is not ideal for standard assembly. A 6 mm hole is loose clearance and will let the bolt rattle slightly once tightened. Use 6 mm only if your design requires the extra space for alignment or if you are using a large washer. For normal work, 5.5 mm is the better choice.
What happens if I drill a hole that is too small?
The bolt will not slide through smoothly and may jam partway. Forcing it can bend the bolt or damage the threads. If this happens, drill the hole larger with the correct bit size. You may need to use a slightly larger bolt or accept a loose fit if the hole is now too large.
Do I need a center punch before drilling?
A center punch is not strictly required, but it is strongly recommended. It creates a small dent that guides the drill bit and prevents it from wandering. Without one, your hole may be off-target by several millimeters, which can ruin the fit or alignment of your assembly.
Is 7/32 inch really the same as 5.5 mm?
Not exactly — 7/32 inch is 5.56 mm, which is 0.06 mm larger. In practice, this tiny difference does not matter for most assembly work. The bolt will fit and function normally. Use 7/32 inch when metric bits are not available.
Can I use the same hole size for all metric bolts?
No. Each bolt size has its own clearance hole specification. M4 uses 4.5 mm, M5 uses 5.5 mm, M6 uses 6.5 mm, and so on. Using the wrong size will either jam the bolt or create a sloppy fit. Always check the standard for the specific bolt size you are using.