Mechanical pins are a fundamental class of fasteners and locating devices critical to the assembly and function of machinery. While seemingly simple, their selection is determined by precise engineering principles related to mechanical tolerances and operational requirements. This article provides an overview of different types of pins.
What is a pin？
A pin is a machine component used for positioning during mechanical assembly, connecting parts, and as a safety device to protect against breakage.
Common Materials for Pins
| Types | Materials |
| Pin Shafts | Carbon structural steel: 1035, 1045 Alloy structural steel: 4130, 4140 Copper: C28000, C65500 Stainless steel: 410, 420, 431, 321 |
| Safety Pins | Carbon Structural Steel: 1035, 1045, 1050 Carbon Tool Steel: Grades W1-9, W1-10 |
| Pin Sleeves | Carbon structural steel: 1045 Alloy quenched and tempered steel: 1335 Alloy structural steel: 5140 |
Major Types of Pins
Dowel Pins
Dowel pins are primarily used for workpiece assembly to ensure repeatable and interchangeable positioning of components.
Cylindrical Pins: These are primarily used for positioning but can also be used for connecting purposes. They come in four diameter tolerance classes—m6, h8, h11, and u8—to meet different application requirements. The common installation method is a reamed fit after drilling, which ensures the required assembly accuracy.
Internal Threaded Cylindrical Pins: These are primarily for positioning but can also be used for connecting. The internal thread is for easy removal. There are two types:
Type A is for through holes, and Type B is for blind holes. The only diameter tolerance class is n6. The minimum pin diameter is 6mm. The common installation method is a reamed fit after drilling, ensuring the required assembly accuracy.
Stepped Cylindrical Pins: These are primarily used for positioning but can also be used for connecting. They offer a high degree of customization and can be tailored to specific working conditions and requirements.
Diamond Pins: Diamond pins are mainly used for positioning and are typically used in conjunction with cylindrical pins. When used together, it’s important to orient the diamond pin correctly. The direction of the diamond pin’s tip should be aligned with the circular tangent drawn at the center of the line connecting the centers of the cylindrical and diamond pins.
Slotted Headless Threaded Cylindrical Pins: These are mainly used for positioning but can also be used for connecting. The common installation method is a reamed fit after drilling to ensure the required assembly accuracy. These pins have a large diameter tolerance and low positioning accuracy, so they are mainly used in applications that don’t require high-precision positioning.
Spring Pins (Roll Pins): Spring pins are flexible and are held in place by friction against the pinhole walls, preventing them from loosening. They have low pinhole precision requirements and do not need to be reamed, offering good interchangeability and allowing for repeated disassembly and reassembly. They have poor rigidity and are not suitable for high-precision positioning. For large loads, several pins can be nested together, with the gaps of adjacent inner and outer pins offset by 180°. They are used in applications with impact and vibration and can replace some cylindrical pins, taper pins, cotter pins, or clevis pins.
Coiled Spring Pins: Coiled spring pins are made by rolling steel sheets, making them easy to manufacture. They are flexible and do not easily loosen after assembly. They have low drilling precision requirements and can be disassembled and reassembled multiple times. They have poor rigidity and are not suitable for high-precision positioning. They can be used in applications with impact and vibration.
Spring Plungers: Also known as ball plungers or indexing plungers, these have a spring designed within their threads. They are a type of locating pin whose preload force can be adjusted by changing the depth to which they are screwed in.
Spring Indexing Plungers: These are mainly controlled manually to extend and retract the pin, performing functions like indexing, positioning, and stop limiting. They are widely used in various types of machinery, especially for indexing, precise positioning, and stop limiting in jigs and fixtures. They come in various types, including rest position, self-locking, knob, flange, and compact designs.
Taper Pins: Taper pins have a 1:50 taper, matching a tapered reamed hole for easy installation. They are mainly used for positioning but can also be used to fix parts and transmit power. They are often used in applications requiring frequent disassembly. They offer higher positioning accuracy than cylindrical pins and are self-locking when subjected to lateral forces.
Internal Threaded Taper Pins: The threaded hole is for removal, allowing them to be used in blind holes. They have a 1:50 taper, matching a tapered reamed hole. They are easy to install and remove, can be used multiple times, offer higher positioning accuracy than cylindrical pins, and are self-locking. They typically protrude from both sides of the connected part for easier installation and removal.
Screwed Taper Pins: The screw thread is for removal. They have a 1:50 taper, matching a tapered reamed hole. They are easy to install and remove, can be used multiple times, offer higher positioning accuracy than cylindrical pins, and are self-locking. They typically protrude from both sides of the connected part for easier installation and removal.
Connecting and Retaining Pins
These are primarily used to connect parts and prevent loosening.
Clevis Pins: Also known as pin shafts, they are commonly used as hinge shafts and are secured with cotter pins for reliable operation.
Headless Clevis Pins: These are used in hinged connections and are secured at both ends with cotter pins for easy disassembly.
Spring-Loaded Pins: These are used to secure other parts, such as shafts and castellated nuts. This is a very reliable and widely used method.
Cotter Pins: Made from high-quality, rigid steel with good elasticity. Their main function is to prevent nuts or clevis pins from loosening. After inserting a clevis pin into a pinhole or tightening a castellated nut, a cotter pin is inserted into the hole in the clevis pin and/or the slot in the nut, and the cotter pin’s tail is bent open to prevent the pin from coming out or the nut from rotating relative to the bolt.
Closed Pins: These are primarily used in applications requiring high retention, suitable for securing heavy-duty components. Because they are closed at both ends, closed pins have a higher load-bearing capacity, making them ideal for connecting and retaining heavy-duty parts in heavy machinery, vehicles, and equipment.
R-Clips: These have an open design that makes them easy to insert and secure. They come in various specifications depending on the specific application needs. They are typically R-shaped or like a spring, with the exact shape and size determined by the application and design requirements. This shape provides enhanced connection stability and adaptability.
Double-Loop R-Clips: These have an open design that makes them easy to insert and secure. They come in various specifications depending on the specific application needs. They are typically R-shaped or like a spring, with the exact shape and size determined by the application and design requirements. This shape provides enhanced connection stability and adaptability.
Split Taper Pins: They have a 1:50 taper, matching a tapered reamed hole. After being driven into the pinhole, the ends can be slightly spread to prevent loosening, making them suitable for applications with impact and vibration.
Grooved Pins: Three grooves of different shapes and depths are rolled or die-forged along the pin’s length. They are pressed into the pinhole and held in place by friction against the hole walls, preventing them from loosening. They can withstand vibration and variable loads. The pinhole does not need to be reamed, and it can be disassembled and reassembled multiple times.
Pins with a Pilot Section and Full-Length Parallel Grooves / Pins with a Chamfer and Full-Length Parallel Grooves: With full-length parallel grooves and a pilot section or chamfer at the end, the pressure between the pin and the hole wall is more evenly distributed. They are suitable for applications with severe vibration and impact.
Pins with a Central Groove 1/3 the Length / Pins with a Central Groove 1/2 the Length: The short groove in the middle is 1/3 or 1/2 of the total length. They are commonly used as arbors to secure parts with a hub at the grooved section.
Full-Length Taper Grooved Pins / Half-Length Taper Grooved Pins / Half-Length Reversed Taper Grooved Pins: The grooves are wedge-shaped, acting similarly to taper pins, but the pressure distribution between the pin and the hole wall is uneven. They are easier to install and remove than taper pins but have lower positioning accuracy. They are often used as shafts.
Round-Head Grooved Pins / Countersunk-Head Grooved Pins: These can replace rivets or screws and are used for securing nameplates, pipe clamps, etc.
Safety Pins
Safety pins have a simple structure and come in various forms. A groove can be cut into the pin for specific applications. To prevent damage to the whole wall if the pin breaks, a pin sleeve can be added inside the hole. They are used for overload protection in transmission devices and machines, acting as shear elements in safety couplings.
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