Metric vs Inch Bolt Patterns: Avoid False 'Matches' From Rounding
Metric and inch bolt-pattern listings often describe the same nominal PCD in different units. They can also make different patterns look interchangeable after rounding. Before buying a wheel or attempting a test fit, normalize the notation, compare the actual geometry, and treat PCD as only one part of the fitment decision.
Define the decision
The question is not simply “Do these numbers look close?” It is:
Does the wheel’s bolt pattern match the hub’s bolt count and PCD closely enough for the intended hardware and application, with no unresolved fitment blockers?
A PCD is normally written as:
- 4x100 — four bolt holes on a 100 mm pitch circle diameter
- 5x114.3 — five bolt holes on a 114.3 mm pitch circle
- 5x4.5 — five bolt holes on a 4.5-inch pitch circle
The first number is the bolt or hole count. The second is the pitch circle diameter, or PCD. Metric and inch versions may be equivalent, but only after conversion.
PCD does not confirm:
- Center-bore compatibility
- Correct bolt or nut thread
- Correct wheel-hole seat type
- Brake-caliper and suspension clearance
- Sufficient load capacity
- Suitable offset and width
- Clearance within the vehicle’s OEM envelope
A wheel is not a confirmed fit because its PCD alone appears similar.
Gather and normalize the specifications
Collect the specifications for both the hub and the wheel from structured fitment data, manufacturer documentation, or direct measurement where necessary.
At minimum, record:
| Specification | Hub requirement | Wheel specification |
|---|---|---|
| Bolt or hole count | Required count | Actual count |
| PCD | Metric or inch value | Metric or inch value |
| Center bore | Hub pilot diameter | Wheel center-bore diameter |
| Fastener specification | Thread, diameter, seat | Hole and seat design |
| Offset and width | OEM envelope requirement | Wheel dimensions |
| Clearance | Brake and suspension limits | Wheel profile and spoke shape |
Convert inch values to millimeters with:
millimeters = inches × 25.4
Convert millimeters to inches with:
inches = millimeters ÷ 25.4
Keep enough decimal places during the calculation. Round only when displaying the result.
Common nominal conversions include:
| Inch PCD | Converted PCD |
|---|---|
| 4.00 in | 101.60 mm |
| 4.25 in | 107.95 mm |
| 4.50 in | 114.30 mm |
| 4.75 in | 120.65 mm |
| 5.00 in | 127.00 mm |
| 5.50 in | 139.70 mm |
| 6.00 in | 152.40 mm |
Thus, 5x4.5 and 5x114.3 are normally two ways of expressing the same nominal pattern. 4x4.00 and 4x100 are not the same nominal PCD: 4.00 inches converts to 101.6 mm.
Beware rounded labels
A listing may display a rounded value such as 4x4.25 for a nominal 108 mm pattern because 4.25 inches equals 107.95 mm. That small difference is caused by the unit conversion and display convention, not necessarily by a different hole layout.
The reverse problem is also possible. A poorly rounded or incorrectly entered listing can make a genuinely different PCD look close to a known pattern. For example, converting 100 mm to inches gives approximately 3.937 inches. A listing that says 3.94 in may be an inch-rounded representation of 100 mm, but the source should still be checked rather than assumed.
Do not use visual similarity or a rounded inch value as the final decision.
Apply hard-blocker checks first
Reject or pause the fitment before detailed comparison if any of these conditions is unresolved:
- Bolt count differs.
A five-hole wheel is not a direct fit on a four-hole hub, regardless of how close the PCD values are.
- Normalized PCD is not the same nominal pattern.
Do not force bolts into holes or rely on tapered hardware to compensate for a PCD mismatch.
- The wheel cannot seat correctly on the hub.
A center bore smaller than the hub pilot will not pass over it. A larger center bore may require an appropriate locating solution, but it does not correct a PCD mismatch.
- Fastener specifications do not match.
Check thread diameter, pitch, stud or bolt arrangement, usable thread engagement, and the wheel’s required seat type. Conical and spherical seats are not interchangeable merely because the fastener fits the thread.
- The wheel fails physical clearance checks.
Brake calipers, suspension components, hub features, and the wheel’s inner barrel and spokes all matter.
A hub-centric ring, different fastener, or spacer may address a specific secondary issue in some applications. None should be treated as a general solution for an incorrect PCD.
Compare the geometry, not just the labels
For a reliable comparison, enter both patterns into a calculator using:
- Hole count
- PCD in millimeters
- Measurement reference, if supplied
- Wheel and hub data from the same fitment record where possible
The PCD describes the circle passing through the centers of the holes or studs. It is not the distance from the outside edge of one hole to the outside edge of another.
If you are measuring a wheel or hub, identify the hole centers accurately. For a four- or six-hole pattern, opposite hole centers can be measured across the circle. For a five-hole pattern, opposite holes do not exist, so measure the center-to-center distance between adjacent holes and calculate the PCD from the chord:
PCD = adjacent center distance ÷ sin(180° ÷ bolt count)
For five holes:
PCD ≈ adjacent center distance × 1.7013
A measurement taken from hole edges instead of hole centers introduces the hole diameter into the result and can produce a convincing but incorrect match. If the holes are chamfered, elongated, damaged, or difficult to center, physical measurement may not be precise enough to establish compatibility.
Assess the source quality
Compare the result with supporting evidence:
- OEM fitment records
- Wheel manufacturer drawings
- A verified part number
- A clear wheel stamp or casting mark
- A direct measurement made with suitable tools
- A known-good hub or wheel used as a reference
Treat marketplace listings, shorthand descriptions, and copied specifications as lower-confidence evidence, particularly when the same wheel is listed with both metric and inch PCD values that do not convert consistently.
Identify uncertainty explicitly
Do not collapse uncertain information into a yes-or-no answer. Record what is known and what remains unverified.
A useful status table is:
| Item | Result | Confidence |
|---|---|---|
| Bolt count | Same / different | High if physically verified |
| PCD after conversion | Same nominal pattern / unresolved | High only with reliable data |
| Center bore | Clears hub / too small / unknown | Depends on measurements |
| Fastener seat and thread | Matches / does not match / unknown | Requires wheel and vehicle data |
| Brake and suspension clearance | Verified / untested | Physical check required |
| Offset and width | Within OEM envelope / unknown | Requires complete wheel data |
A small difference caused only by expressing a nominal value in another unit is not the same as an unexplained PCD discrepancy. For example, 4.25 in converting to 107.95 mm can reasonably correspond to a nominal 108 mm listing. By contrast, a source that alternates between 100 mm and 4.00 in contains a meaningful discrepancy because 4.00 inches equals 101.60 mm.
There is no universal “close enough” rule that makes every near-match safe. Acceptable dimensional variation depends on the wheel, hub, fastener system, and manufacturer’s design. If the source does not state the intended nominal pattern clearly, ask for a drawing or measure the part rather than inferring compatibility from rounding.
Turn the result into a purchase or test-fit action
Use the following workflow before ordering:
- Write both patterns in a consistent form, such as 5 × PCD in mm.
- Convert inch values using 25.4 and retain the unrounded calculation.
- Confirm the bolt count.
- Decide whether any difference is only a unit-display effect or an actual unresolved discrepancy.
- Check center bore, fastener thread and seat, offset, width, load rating, and clearance.
- Confirm the wheel remains inside the vehicle’s OEM envelope.
- Request missing drawings or measurements from the seller or manufacturer.
- If all key specifications match, perform a careful physical test fit before final installation.
During a test fit, install the wheel without forcing it. Confirm that it seats fully against the hub, the center bore clears, the fasteners engage correctly by hand, and the wheel rotates without contact. Do not use impact tools to pull a mismatched wheel onto the hub. If a bolt enters at an angle, the wheel does not sit flush, or the fasteners do not achieve proper engagement, stop.
The safe conclusion is not “the numbers are close.” It is “the nominal PCD is confirmed, the supporting specifications agree, and the physical fit has been verified.”