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Metric Taper Pin Size Chart (ISO 2339, 1:50 Taper)

Guide · Updated October 28, 2026

A metric taper pin is a solid pin ground or turned to a 1:50 taper on diameter. Driven into a reamed taper hole it locks tight, holds position, and can be knocked out and refitted in the same spot, which is why it is used to locate gibs, collars, levers, handwheels and fixture plates. ISO 2339 (also EN 22339, formerly DIN 1) covers unhardened pins from 0.6 to 50 mm. The size, minimum diameter and end radius figures below agree between the fasten.it ISO 2339 table, the Global Fastener ISO 2339 table and the RoyMech taper pin table, and match the ISO 2339:1986 preview. Check the current edition or your pin supplier for critical work.

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Step by step

Pick the pin size: The ISO 2339 size is the small end diameter d. Choose a pin about one quarter of the shaft diameter for a cross pin, or to suit the part for a locating pin.
Pick the length: Choose a standard length that passes through both parts with a little showing at each end.
Work out the big end: Big end diameter = d + l / 50. A 6 x 40 pin is 6.0 mm at the small end and 6.8 mm at the big end.
Drill the pilot: Drill both parts together, clamped, at or just under the small end diameter d.
Ream the taper: Ream with a 1:50 taper pin reamer from the big end side. Stop often and try the pin.
Seat the pin: The pin should go in by hand to about 80 percent of its length. Tap it home with a soft hammer so the ends stand about flush.

ISO 2339 taper pin dimensions (mm)

Columns are: nominal size d (small end), d max (equal to nominal, tolerance h10), d min, and the approximate end dimension a. The pin ends are domed: the end radius is roughly a/2 + d + (0.02 l)² / (8a). Diameter d is measured at the small end; the big end is larger by l / 50.

Size d | d max (h10) | d min | End a (≈)
0.6 | 0.6 | 0.56 | 0.08
0.8 | 0.8 | 0.76 | 0.10
1 | 1 | 0.96 | 0.12
1.2 | 1.2 | 1.16 | 0.16
1.5 | 1.5 | 1.46 | 0.20
2 | 2 | 1.96 | 0.25
2.5 | 2.5 | 2.46 | 0.30
3 | 3 | 2.96 | 0.40
4 | 4 | 3.952 | 0.50
5 | 5 | 4.952 | 0.63
6 | 6 | 5.952 | 0.80
8 | 8 | 7.942 | 1.00
10 | 10 | 9.942 | 1.20
12 | 12 | 11.93 | 1.60
16 | 16 | 15.93 | 2.00
20 | 20 | 19.916 | 2.50
25 | 25 | 24.916 | 3.00
30 | 30 | 29.916 | 4.00
40 | 40 | 39.9 | 5.00
50 | 50 | 49.9 | 6.30

Standard lengths l run 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 120, 140, 160, 180 and 200 mm, then in 20 mm steps. Length tolerance is ±0.25 mm to 10 mm, ±0.5 mm from 12 to 50 mm and ±0.75 mm above 50 mm. Not every length is stocked in every diameter: small pins stop short and large pins start long, so check the supplier range.

The 1:50 taper in numbers

Taper 1:50 on diameter means D − d = l / 50. Per side that is 0.01 mm per mm of length. The included angle is about 1° 8′ 45″ (1.146°), and the half angle about 0.573°. The angle is small enough to self-lock, so a well-fitted pin will not back out under vibration.

Worked example: pinning a collar to a 25 mm shaft

Use a 6 mm pin, about one quarter of the shaft. The pin must pass through the collar and shaft, so for a 40 mm collar pick l = 40. The big end is 6 + 40 / 50 = 6.8 mm. Clamp the collar in place, drill through at 5.8 to 6.0 mm, then ream with a size 6 taper pin reamer from the big end side. Ream until the pin enters by hand to about 32 mm, then tap it home. A 1:50 pin moves in 0.5 mm for every 0.01 mm of diameter you take out, so ream in small bites.

Worked example: checking a pin you found in a drawer

A pin measures 7.96 mm at the small end, 8.96 mm at the big end and is 50 mm long. The diameter change is 1.00 mm over 50 mm, so it is a 1:50 metric pin. The small end sits in the 8 mm row (7.942 to 8.0), so it is an ISO 2339 8 x 50 pin. If the change had been about 1.04 mm over 50 mm, it would be an inch pin with a 1/4 inch per foot taper.

Metric vs inch taper pins

Metric pins use 1:50 on diameter and are named by the small end. Inch pins to ASME B18.8.2 use 1/4 inch per foot (1:48) and are named by a number (7/0 to 14) tied to the big end. The tapers are close but not the same, so do not mix reamers. See the inch taper pin chart for number sizes. For pins that do not need a reamed hole, see slotted spring pins and coiled spring pins.

Common problems

Pin goes in too far: the hole is reamed oversize. Use a longer pin of the same size, or step up one size and ream again.
Pin stands proud and will not seat: the reamer did not go deep enough. Ream a little more and retry.
Pin loosens: the two parts were reamed separately and the holes do not line up. Always ream both parts together, clamped.
Reamer chatters: feed too light or the hole is not drilled close to size. Step drill first on large pins.

FAQ

What taper do metric taper pins have?

1:50 on diameter. The diameter grows 1 mm for every 50 mm of length, or 0.02 mm per mm. That is about 1.15 degrees included angle.

Is the taper pin size the big end or small end?

The small end. ISO 2339 names the pin by its small end diameter d, made to h10 so it is never oversize. Inch taper pins (ASME B18.8.2) are named by the big end instead.

What are type A and type B taper pins?

Type A pins are ground, about Ra 0.8 µm. Type B pins are turned, about Ra 3.2 µm. Dimensions are the same.

How far should a taper pin go in by hand?

Ream until the pin enters by hand to roughly 75 to 80 percent of its length, then drive it home. That leaves enough draw to lock it 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:

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