Dowel Pin Size & Fit Chart — Metric & Inch

Dowel pin size and fit lookup

Search the chart by nominal pin diameter, then filter metric or inch rows and select press, transition/locating, or slip references. The chart keeps the pin tolerance, hole tolerance, reamed-hole range, and fit assumption in separate fields so you can see what the recommendation actually depends on.

MECHANITEC / ENGINEERING REFERENCE

Dowel Pin Size and Fit Chart — Metric and Inch

A bounded reference for precision dowel-pin diameter classes, reamed-hole ranges, and fit assumptions for locating, press, and slip applications.

1–7 of 7 matching rows (7 total)

Dowel Pin Size and Fit Chart — Metric and Inch — page 1 of 1
System	Nominal pin diameter	Nominal diameter (mm)	Nominal diameter (in)	Pin standard/family	Pin tolerance	Fit type	Hole tolerance	Hole minimum (mm)	Hole maximum (mm)	Hole minimum (in)	Hole maximum (in)	Reamer/hole reference	Common lengths	End style	Fit assumption	Governing standard	Source/cross-check	Value status
metric	6 mm	6	0.2362	Hardened ground dowel	m6; 6.004–6.012 mm	transition/locating	H7; 6.000–6.012 mm	6	6.012	0.2362	0.2367	6 mm H7 reamed hole	6–60 mm	Chamfered or radiused; confirm product	m6 pin with H7 hole can range from light interference to clearance; it is a locating/transition reference, not a guaranteed press fit.	ISO 8734:1997 / DIN 6325	ISO 8734 record; EKINSUN m6/H7 cross-check	Bounded reference row; verify selected supplier and drawing.
metric	6 mm	6	0.2362	Precision parallel pin	h6; assumption 5.992–6.000 mm	slip	G7; 6.004–6.016 mm	6.004	6.016	0.2364	0.2369	6 mm G7 reamed hole	6–60 mm	Chamfered or radiused; confirm product	h6 pin and G7 hole; stated limits provide positive clearance under this bounded assumption.	ISO 286 fit classes with ISO 8734 family	EKINSUN G7 guidance; fit-clearance formula	Calculated fit example; verify exact ISO 286 limits and supplier pin class.
metric	8 mm	8	0.315	Hardened ground dowel	m6; 8.006–8.015 mm	press	P7; 7.976–7.990 mm	7.976	7.99	0.314	0.3146	8 mm P7 press-fit hole	8–80 mm	Chamfered or radiused; confirm product	m6 pin and P7 hole; bounded envelope gives interference under the displayed source limits.	ISO 8734:1997 / ISO 286	EKINSUN m6 row; Baetro P7 cross-check	Bounded press reference; verify licensed fit table and assembly force.
metric	8 mm	8	0.315	Hardened ground dowel	m6; 8.006–8.015 mm	transition/locating	H7; 8.000–8.015 mm	8	8.015	0.315	0.3156	8 mm H7 reamed hole	8–80 mm	Chamfered or radiused; confirm product	m6 pin with H7 hole can range from light interference to clearance; use for locating only when the drawing accepts that envelope.	ISO 8734:1997 / DIN 6325	ISO 8734 record; EKINSUN m6/H7 cross-check	Bounded reference row; verify selected supplier and drawing.
metric	12 mm	12	0.4724	Hardened ground dowel	m6; 12.007–12.018 mm	press	P7; 11.971–11.989 mm	11.971	11.989	0.4713	0.472	12 mm P7 press-fit hole	12–120 mm	Chamfered or radiused; confirm product	m6 pin and P7 hole; bounded envelope gives interference under the displayed source limits.	ISO 8734:1997 / ISO 286	EKINSUN m6 row; Baetro P7 cross-check	Bounded press reference; verify licensed fit table and assembly force.
inch	1/4 in	6.35	0.25	Solid dowel pin	ASME B18.8.2 reference; nominal +0.0002 in manufacturer cross-check	transition/locating	+0.0000 / +0.0002 in reference	6.35	6.355	0.25	0.2502	1/4 in nominal reamed hole	1/2–3 in	Type A chamfered reference	ASME-family nominal and hole range only; actual pin limits and assembly force must be checked against the purchased pin.	ASME B18.8.2-2020	ASME record; Baetro/RivCut inch cross-check	Bounded inch reference; verify current product drawing.
inch	1/2 in	12.7	0.5	Solid dowel pin	ASME B18.8.2 reference; nominal +0.0002 in manufacturer cross-check	transition/locating	+0.0000 / +0.0003 in reference	12.7	12.708	0.5	0.5003	1/2 in nominal reamed hole	3/4–4 in	Type A chamfered reference	ASME-family nominal and hole range only; actual pin limits and assembly force must be checked against the purchased pin.	ASME B18.8.2-2020	ASME record; Baetro/RivCut inch cross-check	Bounded inch reference; verify current product drawing.

Search and sort apply to all 7 rows. Print and CSV include only the 7 rows shown on this page.

The metric examples use hardened ground dowel-pin families related to ISO 8734 and DIN 6325. The inch examples are bounded ASME B18.8.2 references cross-checked against manufacturer tables. The selected product drawing and the assembly drawing control when their limits differ.

Why nominal diameter is not enough

A 6 mm dowel pin is not one exact size. An m6 pin has a positive tolerance zone, while an h6 pin has a different zone. The mating hole also has a tolerance zone. The fit is the result of comparing those two zones, not a label attached to the nominal diameter.

For each row, compare the smallest hole with the largest pin and the largest hole with the smallest pin. The first comparison shows the tightest possible clearance, or the greatest interference when the result is negative. The second shows the loosest possible clearance. This range is more useful than saying that a pin is simply “press fit” or “slip fit.”

Press, transition, and slip references

The chart uses three different reference types:

Press: The bounded 8 mm and 12 mm examples pair an m6 pin with a P7 hole. The displayed limits produce interference under the stated assumptions. Installation force, material, wall thickness, lubrication, and blind-hole air relief still matter.
Transition/locating: An m6 pin in an H7 hole can range from light interference to clearance. It is a common locating reference, but it is not a guarantee that every combination will assemble by hand or retain the pin permanently.
Slip: The 6 mm example pairs an h6 pin with a G7 hole. The positive clearance shown is conditional on those tolerance classes and on a correctly reamed hole.

Do not turn a locating reference into a universal assembly instruction. If the joint must be removable, specify the hole and pin classes that produce the required minimum clearance. If the joint must retain the pin, specify the maximum installation force and the minimum interference that the materials can support.

Ream the hole when the fit requires it

Drilling creates a hole, but it does not normally establish the roundness, size, and surface condition needed for a precision dowel fit. Drill undersize, then use the specified machine reamer or another qualified process. Measure the finished hole when the fit is important.

Keep chips and cutting fluid out of a blind hole. Provide adequate depth below the pin, a lead-in where required, and an extraction method when the pin must be removed. An extractable dowel with an internal thread may be appropriate for a blind location, but the thread and installation details must come from the selected product standard.

Dowel pins versus spring pins

A precision dowel pin is a solid, close-tolerance locating element. It transfers location through its cylindrical surface and normally requires a prepared hole. A spring pin, roll pin, or coiled pin is resilient and changes shape as it enters the hole. It is selected for retention and compliance, not as a direct substitute for a ground locating dowel.

Do not replace a dowel with a spring pin because the nominal diameters look similar. The hole tolerance, retention mechanism, shear behavior, installation method, and repeatability are different. Use the applicable spring-pin standard and manufacturer hole recommendation when that is the intended part.

Metric and inch rows

Metric rows preserve millimeter source values and show inch conversions for planning. Inch rows preserve the inch nominal and hole range. The converted values help compare systems, but they do not replace the source-unit callout on a drawing or the tolerance limits in the selected standard.

For the 1/4 in and 1/2 in inch references, treat the hole values as bounded product-family examples. ASME B18.8.2 defines the inch-series pin family, but the actual pin tolerance, chamfer, length, and hole recommendation must be confirmed for the purchased part.

How to specify a dowel fit in CAD

Call out the nominal pin diameter and the pin tolerance or product standard.
Call out the hole tolerance separately for each mating component.
State whether the hole is drilled, reamed, bored, or otherwise finished.
Check the complete tolerance envelope, not only the nominal dimensions.
Check assembly force, wall thickness, blind-hole depth, and extraction access.
Verify the actual supplier certificate or inspection result for production-critical locations.

For a general opening size, compare the clearance hole size chart. For tool selection before reaming, use the drill bit size chart. Those charts do not replace the tolerance-controlled dowel-hole specification.

Sources and limits

The metric pin family follows the ISO 8734:1997 official record, which remains current after confirmation in 2023. The inch pin family follows the ASME B18.8.2-2020 record. Hole-preparation and tolerance-envelope guidance is cross-checked against SPIROL guidance. Standards are licensed; verify the exact row, fit, material, and supplier drawing before release.

Frequently asked questions

Is H7/m6 always a press fit?

No. The tolerance zones can produce interference, transition, or clearance at different limit combinations. Use the complete pin and hole limits. The chart labels H7/m6 as a transition/locating reference.

What hole should I use for an 8 mm dowel pin?

Choose the hole from the required fit. The bounded examples show H7 with an m6 pin for locating and P7 with an m6 pin for a stronger press reference. Confirm the material and assembly requirements before selecting either row.

Can I drill the dowel hole?

Not when the design requires a precision fit. Drill undersize and finish the hole with the specified reamer or qualified machining process, then verify the finished tolerance.