spring pin
A spring pin is a mechanical fastener used to fix the relative position between two or more components of a machine. The main body diameter of the spring pin is larger than the aperture, and one or both ends have chamfers for easy insertion of the pin into the hole. The spring action of the pin allows it to compress when it reaches the aperture. The force applied by the pin to the hole wall fixes it in the hole, so the spring pin is considered a self retaining fastener. There are two types of spring pins: slotted spring pins and spiral spring pins.

Working principle of spring pin
When the spring pin is inserted into the hole, it will compress. Due to its spring like characteristics, the diameter will decrease when inserted into the hole. After installation, the elasticity restores the pin to a stationary state, forcing the outer surface to press against the inner wall of the mating hole. The friction between the two surfaces fixes the pin in place, preventing it from falling off or accidentally shifting.

Roll spring pin
Spiral spring pin.
Rolled spring pin, also known as spiral pin, is a self retaining engineering fastener made by rolling metal strip into a spiral cross-sectional area of 2 and forming+1 ⁄ 4 turns. The main diameter of the rolled spring pin is larger than the recommended aperture, and both ends are chamfered for easy insertion of the pin into the hole. The spring action of the pin allows it to compress when it reaches the aperture.
When installing the rolled spring pin, compression starts from the outer edge and then moves towards the center through the coil. When a load is applied to the pin, the rolled spring pin continues to bend after insertion, providing excellent performance to resist fatigue in dynamic applications. The rolled spring pin was invented by Herman Koehl around 1948.
There are three different types of roll products on the market: standard (ISO 8750), heavy-duty (ISO 8748), and lightweight (ISO 8751), which can provide various combinations of strength, flexibility, and diameter to meet different requirements for the main body materials and performance. Typical materials for rolled spring pins include high carbon steel, stainless steel, and alloy 6150.
Roll up pins are widely used in cosmetic boxes, car door handles and locks, and latches, as hinge pins. They are also used as pivot and shaft, for aligning and stopping, to secure multiple components together (such as gears and shafts), and even as ejector pins to remove motherboards from PCs. The automotive and electrical industries use rolled pins in products such as steering boxes and columns, pumps, electric motors, and circuit breakers.
international standard
Slotted spring pin: ISO 8752
Standard load: UNE–EN-ISO 8750、NASM10971、NASM51923、NAS1407、ASME B18.8.2、ASME B18.8.3M
heavy: UNE–EN-ISO 8748、NASM10971、NASM39086、NAS561、ASME B18.8.2、ASME B18.8.3M
Lightweight: UNE–EN-ISO 8751、NASM10971、NASM51987、NAS1407、ASME B18.8.2、ASME B18.8.3M
The standard spiral spring pin achieves the best balance between flexibility and strength, making it suitable for most applications.
Heavy duty spiral spring pins are typically used for high shear strength applications and hardened matrix materials.
Lightweight dowels are used in applications with soft metal and plastic holes, where the use of traditional press fit solid dowels carries a high risk of enlarging or damaging the host.
Winding spring pin as a positioning pin in aluminum castings
The spiral spring pin fixes the lifting rod relative to the valve stem

Slotted spring pin.
Slotted spring pin is a cylindrical pin made by rolling a strip of material with grooves, which gives the pin a certain degree of flexibility when inserted. Slotted spring pins are also known as rolling pins, Seelock pins, or "C" pins. These are also often referred to as spiral sales - pronounced as' spiril 'in the Birmingham area.
See also
Card spring - type of fastener or retaining ring
Open mouth pin - a metal fastener with two forks that may bend during installation
Spring plunger, a spring-loaded device used to position, locate, or lock components onto pins or balls through spring force

During installation, the spring pin will compress and adapt to the smaller main hole. The compressed pin will exert an outward radial force on the hole wall. The holding force is provided by compression and friction between the pin and the hole wall. Therefore, the surface contact between the pin and the hole is crucial.
Increasing radial stress and/or contact surface area can optimize retention force. Larger and heavier pins will exhibit lower flexibility, resulting in higher spring loads or radial stresses during installation. Coil spring pins are an exception to this rule as they can be used for multiple purposes (light, standard, and heavy) to provide a greater range of strength and flexibility within a given diameter.
How can the diameter of the protruding end of the pin be larger than the hole when the length is less than 60% retained in the main hole. The example on the right shows that the diameter of the protruding end of the pin is approximately equal to the diameter of the hole.
There is a linear relationship between the friction/holding force and the engagement length of the spring pin inside the hole. Therefore, increasing the length of the pin and the resulting contact surface area between the pin and the main hole will result in higher retention force. Due to the presence of chamfers, there is no holding force at the end of the pin, so it is very important to consider the chamfer length when calculating the engagement length. The chamfer of the pin should never be located in the shear plane between the mating holes, as this can cause tangential force to be converted into axial force, resulting in "movement" or the pin moving away from the shear plane until the force is counteracted. To avoid this situation, it is recommended that the distance between the end of the pin and the cutting plane should be one pin diameter or more. This situation may also be caused by conical holes, which can also convert tangential forces into outward motion. Therefore, it is recommended to use non tapered holes, and if taper is required, it should be kept below 1 °.
The chamfer of the pin shall not be located within the shear plane. In this case, the pin will move in the indicated direction until the chamfer is no longer within the shear plane.
The spring pin will restore a portion of its pre installed diameter in areas not supported by the main material. In alignment applications, 60% of the total length of the spring pin should be inserted into the initial hole to permanently fix its position and control the diameter of the protruding end. In the application of free fit hinges, the pins should be left in the external components, provided that the width of these positions is greater than or equal to 1.5 times the diameter of the pins. If this criterion is not met, it may be wise to leave the sales in the central component. Friction fit hinges require all hinge components to be equipped with matching holes, and each component (regardless of the number of hinge segments) should be maximally engaged with the pin.