Taper pins are precision mechanical pins used to locate, align and secure components in engineering assemblies. Unlike a parallel pin, the diameter changes along the length of the pin, allowing the mating components to be located as the pin seats in a corresponding tapered hole.
The following table gives nominal diameter, approximate end dimension a and the available length range contained in the RoyMech reference data. Dimensions are in millimetres.
| Nominal Diameter d (h10) | 0.6 | 0.8 | 1.0 | 1.2 | 1.5 | 2.0 | 2.5 | 3.0 | 4.0 | 5.0 | 6.0 | 8.0 | 10.0 | 12.0 | 16.0 | 20.0 | 25.0 | 30.0 | 40.0 | 50.0 |
| a (approx) | 0.08 | 0.10 | 0.12 | 0.16 | 0.20 | 0.25 | 0.30 | 0.40 | 0.50 | 0.63 | 0.80 | 1.00 | 1.20 | 1.60 | 2.00 | 2.50 | 3.00 | 4.00 | 5.00 | 6.3 |
| Length l (range) | 4–8 | 5–12 | 6–16 | 6–20 | 8–25 | 10–35 | 10–35 | 12–55 | 14–55 | 20–60 | 25–90 | 25–130 | 30–160 | 35–180 | 40–200 | 45–200 | 50–200 | 60–200 | 80–200 | 100–200 |
Metric taper pins to ISO 2339 use a taper of 1:50 on diameter. This means that the diameter changes by 1 mm for every 50 mm of axial length.
The relationship can be written as:
(D - d) / L = 1 / 50
where:
For example, over a length of 100 mm, a 1:50 taper produces a diameter difference of 2 mm.
A taper pin passes through corresponding tapered holes in the mating components. As the pin is inserted, increasing engagement between the tapered surfaces progressively removes clearance and establishes the relative position of the components.
This makes taper pins useful where two parts must be located positively and where the assembly may later need to be dismantled and returned to substantially the same position.
Typical applications can include machine assemblies, levers, hubs, fixtures and other arrangements where positive relative location is required.
The wedging action of a taper pin can provide a secure fit, but it should not automatically be assumed that friction alone provides all the retention needed for every application.
Vibration, alternating loads, shock, temperature changes and repeated disassembly can all affect a pinned joint. Where unintended movement or pin withdrawal would have significant consequences, the complete joint and any required positive retention should be considered explicitly.
The mating hole must have the correct taper and size for the selected pin. A normal parallel drilled hole does not provide the required seating surface.
A typical manufacturing sequence is to produce a suitable preliminary hole and then finish the taper using the appropriate taper-pin reamer. The exact preparation method, allowance and tooling depend on pin size, material, production method and the reamer manufacturer's recommendations.
Where two assembled components are to be located together, producing the tapered hole through the components in their required assembled position can establish their relative location directly.
Taper-pin reamers are designed to produce the corresponding tapered hole for the pin. Hand and machine reamers are available, and the correct tool should be selected for the pin standard, nominal size and manufacturing method.
ISO publishes separate standards covering taper-pin reamers. For example, ISO 3467 covers machine taper-pin reamers with Morse taper shanks intended to produce holes for taper pins manufactured to ISO 2339.
Do not assume that the nominal designation of a reamer is simply the measured diameter at one arbitrary point on the cutting tool. Use the reamer manufacturer's dimensional data and the applicable tooling standard when selecting the tool.
A taper pin has a small end and a large end, so assembly direction is an important part of the design. The surrounding components should provide access for installation and, where maintenance is required, for subsequent removal.
A plain taper pin is normally removed by applying force from the smaller end towards the larger end. If the small end becomes inaccessible after assembly, future dismantling can become unnecessarily difficult.
Where access for driving out a plain pin is impractical, other taper-pin forms, including pins with internal or external threads, may provide a more suitable arrangement.
| Consideration | Taper Pin | Parallel Dowel |
|---|---|---|
| Geometry | Diameter changes along the pin length | Parallel cylindrical diameter |
| Mating hole | Corresponding tapered hole | Accurately sized parallel hole |
| Location | Clearance is progressively removed as the pin seats | Controlled by the relationship between dowel and hole dimensions and fits |
| Assembly direction | Defined by the taper | Normally not directional unless the design provides another feature |
| Removal | Access to the small end is important for a plain pin | Depends on fit and the accessibility of the dowel |
| Hole manufacture | Requires the corresponding taper | Requires an accurately sized parallel hole |
Neither arrangement is universally preferable. The choice depends on required location accuracy, manufacturing method, assembly sequence, maintenance, loading and production requirements.
A taper pin can transmit load between components, but its suitability should not be judged solely from the fact that the pin seats tightly.
Where significant torque or transverse load must pass through the pin, the pin and surrounding components should be assessed for the actual loading. Relevant considerations can include pin shear, bearing or contact stress in the mating components, section thickness, edge distance, fatigue and the effect of the hole on the components.
For heavily loaded shaft-to-hub torque transmission, a key, spline or another purpose-designed shaft connection may be more appropriate.
The dimensions on this page are for the metric 1:50 taper-pin system associated with ISO 2339.
Imperial taper pins are also encountered in existing machinery and use different standards and dimensional systems. A commonly encountered inch taper-pin system uses a taper of 1:48 on diameter, equivalent to a change of 1/4 inch per foot.
ISO 2339:1986 – Taper pins, unhardened.
This is the current ISO standard for unhardened taper pins with metric
dimensions and nominal diameters from 0.6 mm up to and including 50 mm.
ISO records the standard as current following confirmation in 2022.
BS EN 22339:1992 – Taper pins, unhardened
(ISO 2339:1986).
This is the British/European adoption of ISO 2339 for unhardened taper pins.
ISO 3465, ISO 3466 and ISO 3467.
These standards cover different forms of metric taper-pin reamers. Select
the applicable tooling standard according to whether a hand or machine reamer
and the relevant shank arrangement are required.