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Reference Chart

Dowel Pin Size Chart

Reference chart for standard and oversized dowel pin dimensions with recommended hole sizes and tolerances. Covers 1/16" through 3/4" standard pins, oversized (+0.001") variants, and M2 through M16 metric pins per ASME B18.8.2.

Showing 27 of 27 pins
Pin Diameter ▲ Pin Length Range ▲ Hole Size (Ream) ▲ Hole Tolerance ▲ Chamfer ▲ Material ▲
1/16"3/16" – 1/2"0.0625"+0.0000 / +0.00020.015"Alloy Steel, RC 60
3/32"1/4" – 3/4"0.0938"+0.0000 / +0.00020.015"Alloy Steel, RC 60
1/8"1/4" – 1-1/2"0.1250"+0.0000 / +0.00020.015"Alloy Steel, RC 60
5/32"3/8" – 1-1/2"0.1563"+0.0000 / +0.00020.015"Alloy Steel, RC 60
3/16"3/8" – 2"0.1875"+0.0000 / +0.00020.015"Alloy Steel, RC 60
1/4"1/2" – 3"0.2500"+0.0000 / +0.00020.020"Alloy Steel, RC 60
5/16"1/2" – 3"0.3125"+0.0000 / +0.00020.020"Alloy Steel, RC 60
3/8"3/4" – 3"0.3750"+0.0000 / +0.00030.025"Alloy Steel, RC 60
7/16"3/4" – 3"0.4375"+0.0000 / +0.00030.025"Alloy Steel, RC 60
1/2"3/4" – 4"0.5000"+0.0000 / +0.00030.030"Alloy Steel, RC 60
5/8"1" – 4"0.6250"+0.0000 / +0.00030.030"Alloy Steel, RC 60
3/4"1" – 4"0.7500"+0.0000 / +0.00040.035"Alloy Steel, RC 60
1/8" (+0.001)1/4" – 1-1/2"0.1260"+0.0000 / +0.00020.015"Alloy Steel, RC 60
3/16" (+0.001)3/8" – 2"0.1885"+0.0000 / +0.00020.015"Alloy Steel, RC 60
1/4" (+0.001)1/2" – 3"0.2510"+0.0000 / +0.00020.020"Alloy Steel, RC 60
5/16" (+0.001)1/2" – 3"0.3135"+0.0000 / +0.00020.020"Alloy Steel, RC 60
3/8" (+0.001)3/4" – 3"0.3760"+0.0000 / +0.00030.025"Alloy Steel, RC 60
1/2" (+0.001)3/4" – 4"0.5010"+0.0000 / +0.00030.030"Alloy Steel, RC 60
5/8" (+0.001)1" – 4"0.6260"+0.0000 / +0.00030.030"Alloy Steel, RC 60
3/4" (+0.001)1" – 4"0.7510"+0.0000 / +0.00040.035"Alloy Steel, RC 60
M26 – 16 mm2.000 mm+0.000 / +0.0060.3 mmAlloy Steel, 58 HRC
M38 – 24 mm3.000 mm+0.000 / +0.0060.4 mmAlloy Steel, 58 HRC
M410 – 32 mm4.000 mm+0.000 / +0.0080.5 mmAlloy Steel, 58 HRC
M512 – 40 mm5.000 mm+0.000 / +0.0080.5 mmAlloy Steel, 58 HRC
M614 – 50 mm6.000 mm+0.000 / +0.0080.6 mmAlloy Steel, 58 HRC
M816 – 60 mm8.000 mm+0.000 / +0.0090.8 mmAlloy Steel, 58 HRC
M1020 – 80 mm10.000 mm+0.000 / +0.0091.0 mmAlloy Steel, 58 HRC
M1224 – 100 mm12.000 mm+0.000 / +0.0111.2 mmAlloy Steel, 58 HRC
M1632 – 120 mm16.000 mm+0.000 / +0.0111.5 mmAlloy Steel, 58 HRC
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Quick Answer: What Hole Size Do I Ream for a Dowel Pin?

A dowel pin is a precision ground cylinder that locates and aligns two parts. For a press fit, ream the hole to the nominal pin diameter with a tight plus tolerance so the slightly oversized pin creates an interference fit. A 1/4″ pin needs a 0.2500″ hole reamed to +0.0000 / +0.0002″. Holes must be reamed, not just drilled.

This chart lists dowel pin dimensions per ASME B18.8.2 with: pin diameter, pin length range, reamed hole size, hole tolerance, chamfer and material. Inputs include the nominal pin diameter and whether you need a standard, oversized (+0.001″) or metric pin. Search by pin diameter.

Common sizes: 1/8″ → 0.1250″ hole (+0.0000 / +0.0002) | 1/4″ → 0.2500″ hole (+0.0000 / +0.0002) | 1/2″ → 0.5000″ hole (+0.0000 / +0.0003) | M6 → 6.000 mm hole | oversized adds 0.001″ for worn-hole repair | alloy steel RC 60.

Notes on This Chart

  • Standard dowel pin dimensions per ASME B18.8.2.
  • Pin diameter tolerance is typically +0.0001 / +0.0003" for standard pins.
  • Oversized pins are 0.001" larger for repair or tighter press fits.
  • Metric dowel pins per ISO 2338 (unhardened) and ISO 8734 (hardened).
  • Always ream holes; do not rely on drilled hole size for press fits. Refer to our drill bit size chart for the correct undersize drill before reaming.
  • For blind dowel holes, specify a flat-ground vent or a pull-dowel pin to prevent air compression lock during insertion.

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Frequently Asked Questions

What is the correct hole size for a dowel pin?

For a standard press-fit dowel pin, the hole should be reamed to the exact nominal pin diameter with a tolerance of +0.0000 / +0.0002 inches. For example, a 1/4 inch dowel pin requires a 0.2500 to 0.2502 inch reamed hole. The interference fit between the slightly oversized pin and the hole creates a secure press fit.

What is the difference between standard and oversized dowel pins?

Standard dowel pins are manufactured to the nominal diameter with a plus tolerance (typically +0.0001 to +0.0003 inches). Oversized dowel pins are 0.001 inches larger than nominal and are used to repair worn holes or when a tighter fit is needed. They are designated with an "O" suffix.

How do I remove a press-fit dowel pin?

Press-fit dowel pins can be removed using a pin punch and hammer, driving the pin out from the opposite side. For blind holes, use a dowel pin extractor or puller tool. Avoid damaging the reamed hole surface during removal, as this can affect the fit of a replacement pin.

What material are dowel pins typically made from?

Standard dowel pins are made from alloy steel, heat treated to Rockwell C60 minimum hardness per ASME B18.8.2. Stainless steel (18-8 or 416) dowel pins are available for corrosion-resistant applications. The ground and polished finish ensures consistent diameter and surface quality.

Should dowel pin holes be drilled or reamed?

Dowel pin holes must be reamed, not just drilled. A drill produces a hole that is typically oversized and has a rough surface finish. Reaming produces a precise diameter with a smooth finish that allows proper interference fit. Always drill undersized first, then ream to final size.

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