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Inch Slotted Spring Pin Size Chart (ASME B18.8.2)

Guide · Updated October 28, 2026

A slotted spring pin, or roll pin, is a strip of hardened spring steel or stainless rolled into a tube with a lengthwise slot. It is made a few thousandths over the hole, so it closes up as you drive it and holds by spring pressure against the bore. In inch sizes it is covered by ASME B18.8.2, the same standard that covers taper, dowel, straight and grooved pins. The chart below gives the 1/16 to 1/2 in sizes. The figures match across three published copies of the B18.8.2 table: Engineers Edge, the H&B spec sheet, and the Global Fastener standard page.

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Step by step

  1. Pick the nominal size: Pick the nominal size from the load and the room you have. On inch roll pins the nominal size is the basic pin and hole size, so a 1/4 pin goes in a 1/4 hole.
  2. Drill to the recommended hole: Drill the hole inside the recommended range in the chart. For a 1/4 pin that is .250 to .256 in, so a sharp 1/4 jobber drill in good condition usually lands in range.
  3. Check the hole: Check the hole with pin gages. The low limit should go and anything over the high limit should not, or the pin will lose its grip.
  4. Check the pin: Mike the pin before it goes in. Its free diameter is larger than the hole, for example .258 to .264 in on a 1/4 pin, so it compresses as it is driven.
  5. Drive with a roll pin punch: Start the chamfered end and drive the pin with a roll pin punch that has a pilot nub, so the end does not mushroom or split.
  6. Orient the slot: In a shear joint, turn the slot away from the load, toward the neutral side, so the full wall carries the shear.

ASME B18.8.2 slotted spring pin dimensions (inches)

Columns are: nominal size, basic diameter, pin diameter before fitting (min–max), basic wall thickness, recommended hole (min–max), and minimum double shear load in pounds. The first load column is for SAE 1070-1095 carbon steel and type 420 stainless. The second is for 300 series stainless, which is work hardened only and not heat treated.

The maximum pin diameter is checked with a GO ring gage. The minimum is the average of three readings taken along the pin. Length tolerance is ±.015 in up to 1 in long, ±.020 in over 1 to 2 in, ±.025 in over 2 to 3 in and ±.030 in over 3 to 4 in. Common length steps are 1/16 in from 1/8 to 1 in, 1/8 in from 1 to 2 in, and 1/4 in from 2 to 6 in. The standard also lists 9/64, 5/8 and 3/4 in sizes. They are not stocked as widely, so check with your supplier before you design around them.

Hardness and materials

Carbon steel pins are SAE 1070 to 1095 spring steel, hardened to about HRC 46 to 53 in the 5/16 to 1/2 in sizes. Type 420 stainless is hardened too, to about HRC 43 to 52, and it is magnetic. Type 300 stainless pins are not magnetic and are not heat treated, which is why their shear rating is lower. Use 420 when you need strength with some corrosion resistance. Use 300 series in food equipment, wet service or near electronics, and size up if the joint is loaded.

Worked example: roll pin through a 3/4 in shaft

A collar is pinned to a 3/4 in shaft with a 3/16 carbon steel roll pin. The pin crosses the shaft, so it is in double shear. The chart rating is 4,150 lb. The shaft carries 600 in·lb of torque. The force at the pin is the torque divided by the shaft radius: 600 / 0.375 = 1,600 lb. That gives a safety factor of 4,150 / 1,600 = about 2.6. If the pin were 300 series stainless, the rating would drop to 2,425 lb and the factor to about 1.5. That is too thin for shock loads, so you would go up to a 1/4 stainless pin (4,100 lb) or switch to 420.

Check the shaft too. A rule of thumb is to keep the pin diameter at or under about one quarter to one third of the shaft diameter. A 3/16 pin in a 3/4 shaft is exactly one quarter, which leaves plenty of shaft around the hole.

Worked example: picking the drill

For a 5/32 pin the recommended hole is .156 to .160 in. A 5/32 drill is .1562 in, which is right at the bottom of the range. A worn drill or a hole in soft aluminum can cut a few tenths over, which still lands in range. A No. 22 drill (.157 in) also fits. A No. 21 (.159 in) is in range too, but it is close to the top, so the pin will hold with less spring. When in doubt, drill one hole in scrap and check it with pin gages before you drill the part.

Slotted vs coiled vs solid pins

Slotted roll pins are the cheap, common choice. Coiled spring pins (spiral pins) are rolled two and a quarter turns. They spread stress more evenly, take shock and fatigue better and are kinder to soft host parts. Solid dowel pins locate parts accurately but need a reamed hole and a press. In metric work, the slotted pin standard is ISO 8752 (heavy duty) and the coiled pin standard is ISO 8748 (heavy duty). Do not swap inch and metric charts, because the holes are different.

Common problems

FAQ

What size hole for a 1/8 roll pin?

ASME B18.8.2 recommends .125 to .129 in. A 1/8 drill is the normal choice.

What size hole for a 1/4 roll pin?

.250 to .256 in. A sharp 1/4 drill is usually right. Do not use an F drill (.257), which is just over the top limit.

Is a 420 stainless roll pin as strong as carbon steel?

Yes in the chart. ASME B18.8.2 gives SAE 1070-1095 carbon steel and 420 stainless the same minimum double shear load. 300 series stainless is rated lower, about 58% of it.

Can I mix inch and metric roll pins?

No. A 6 mm pin and a 1/4 pin are close but the hole ranges are different, and a metric pin in an inch hole can be loose or too tight.

Pin and retaining-ring size charts

Picking a fastener to locate or retain a part? Compare the other pin and ring charts in this set:

Related guides and calculators

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General shop information only — follow your drawing, tool maker's data and your quality system.