Pins

What are pins?

Pins are simple fasteners used to join, locate, align, or retain parts in engineering assemblies. They are pushed or driven into holes to stop parts moving relative to each other, to hold components on shafts, to act as hinges and pivots, or to lock other fasteners in place. Pins are quick to fit, inexpensive, and reliable, which makes them one of the most widely used fixing methods in machinery, vehicles, tools, and equipment.

Different pins do different jobs. Spring pins and roll pins hold parts together by pressing outwards against the sides of the hole. Dowel pins locate parts accurately. Clevis pins create pivoting joints. Split pins lock nuts and clevis pins so they cannot work loose.

Pins are usually described by:

• Diameter - the nominal diameter of the pin, which usually matches the size of the hole it fits, such as 1.5 mm, 3 mm, 3/16 inch, or 1/4 inch
• Length - the overall length of the pin, such as 6 mm or 1/2 inch
• Type - such as slotted spring pin, coiled spring pin, dowel pin, clevis pin, or split pin
• Duty - such as light, standard, or heavy duty for spring pins
• Material and finish - such as carbon spring steel, stainless steel, plain, black, or nickel finish
• Standard - such as DIN 1481 for heavy duty slotted spring pins, which sets the pin’s dimensions and specification

For example, a 3/16 × 1/2 inch slotted spring pin to DIN 1481 has a nominal 3/16 inch diameter, a 1/2 inch length, and is made from carbon spring steel.

Key features:

• Secure retention - holds parts firmly in place without threads
• Accurate location - dowel pins align parts precisely
• Quick to fit - pressed or driven into place with simple tools
• Vibration resistant - spring pins grip tightly and resist working loose
• Pivot and hinge joints - clevis pins create simple pivoting connections
• Locking - split pins stop nuts and clevis pins coming loose
• Metric and imperial sizes - to suit modern and older equipment
• Range of materials - carbon spring steel, stainless steel, and other options

In simple terms, pins are simple fasteners that hold, locate, and lock parts together quickly and reliably.

Why are pins essential?

Pins are essential because many assemblies need parts to be fixed, aligned, or retained in a simple, compact, and reliable way. Threads take up space, can loosen, and add cost, while welding is permanent. Pins provide a quick, low-cost, and secure alternative that can often be removed when needed. They are particularly useful for fixing gears, pulleys, and collars to shafts, locating machine parts accurately, and creating pivots and hinges.

Their main benefits are:

• Simple, reliable fixing - holds parts securely with no need for threads or adhesives
• Fast assembly - pins can be fitted quickly with a press or pin punch
• Accurate alignment - dowel pins locate parts precisely and repeatably
• Resists vibration - spring pins press outwards against the hole, keeping them firmly in place
• Removable - most pins can be driven out for repairs and maintenance
• Space saving - compact fixings for small and tight assemblies
• Safety - split pins and clips stop critical fasteners and joints coming apart
• Cost-effective - inexpensive parts that perform important jobs

Pins are used across a wide range of industries and applications, including:

• Engineering and machinery - fixing gears, pulleys, collars, and levers to shafts
• Automotive and transport - steering, suspension, brakes, and linkages
• Agricultural machinery - linkages, hitches, implements, and pivots
• Tools and hardware - hammer heads, hinges, handles, and hand tools
• Hydraulic and pneumatic equipment - cylinder mountings, clevises, and linkages
• Manufacturing and assembly - locating jigs, fixtures, and machine parts
• Electrical and electronics - small mechanisms, switches, and assemblies
• Furniture, doors, and gates - hinges and moving parts
• Toys, models, and DIY - small pivots and fixings

The main types of pins

Pins are usually grouped by their design, duty, material, and the job they do.

Spring pins (roll pins):

• Slotted spring pins - rolled from spring steel with a slot along their length. When driven into a slightly smaller hole, the pin compresses and presses outwards against the sides, holding it firmly in place. Common standards include DIN 1481 and ISO 8752 for heavy duty pins, and lighter duty versions for lower loads
• Coiled spring pins - rolled from strip into a spiral of about two and a quarter turns. They spread the load more evenly around the hole, absorb shock and vibration well, and are often more resistant to fatigue than slotted pins. Made in light, standard, and heavy duty versions, to standards such as ISO 8748 and ISO 8750
• Heavy duty spring pins - made from thicker material for higher shear strength and heavy loads
• Light duty spring pins - thinner pins for softer materials, thin sections, and lower loads

Dowel pins:

• Hardened dowel pins - precision ground pins used to locate parts accurately, such as machine components, jigs, and fixtures. Made to standards such as ISO 8734
• Unhardened dowel pins - lower cost dowels for general location work, made to standards such as ISO 2338
• Taper pins - have a slight taper along their length, giving a tight, accurate fit that can be removed and refitted

Clevis and retaining pins:

• Clevis pins - have a head on one end and a hole or groove on the other, used to create pivoting joints in clevises, linkages, and hitches
• Split pins (cotter pins) - bent wire pins that pass through a hole in a bolt, axle, or clevis pin, then have their legs bent apart to lock the part in place
• R-clips and linch pins - quick-release clips used to retain clevis pins and hitch pins, especially on agricultural equipment
• Hitch pins - strong pins used to connect implements, trailers, and attachments

Other pins:

• Grooved pins - solid pins with grooves along their length that create a tight fit in a plain hole
• Ball lock and quick release pins - pins with spring-loaded balls that lock in place and release at the push of a button

By material:

• Carbon spring steel - strong and economical, the standard material for most spring pins, usually supplied plain, black, or with a protective finish
• Stainless steel - such as AISI 304 and 420 grades, resisting rust and corrosion for wet, food, marine, and outdoor environments
• Hardened steel - used for dowel pins to give accurate, wear-resistant location
• Brass and other materials - for special applications

By finish:

• Plain or self-colour - uncoated, usually lightly oiled
• Black - a dark oxide or phosphate finish with light corrosion protection
• Zinc plated - a silver finish with good corrosion protection for general use
• Nickel or stainless finish - for improved corrosion resistance and appearance

By size system:

• Metric pins - sized in millimetres, such as 1.5 × 6 mm or 4 × 20 mm
• Imperial pins - sized in inches, such as 3/16 × 1/2 inch or 1/4 × 1 inch

How to choose the right pins?

Choosing the right pin means matching it to the hole, the load, and the job it needs to do. Work through these points in order:

• Job type - choose spring pins for retaining parts, dowel pins for accurate location, clevis pins for pivots, and split pins or R-clips for locking
• Hole size - choose a spring pin with a nominal diameter that matches the hole. Spring pins are made slightly oversize so they compress and grip when fitted
• Length - choose a length that passes through the parts fully, without sticking out where it could catch or cause harm
• Load - choose heavy duty spring pins for higher loads and shock, and light duty pins for soft materials or thin sections
• Slotted or coiled - choose slotted pins for general use, and coiled pins where vibration, shock, and fatigue are a concern, or where a more even fit is needed
• Material hardness - in soft materials such as aluminium or plastic, lighter duty pins reduce the risk of damaging the hole
• Accuracy - choose hardened dowel pins in accurately reamed holes for precise location
• Material - choose carbon spring steel for general use, and stainless steel for wet, marine, food, or corrosive environments
• Metric or imperial - match the pin to the hole size and the equipment it is used on
• Removal - consider whether the pin will need to be removed, and choose a type that can be driven out or released easily
• Quality and brand - choose pins from reputable suppliers for consistent dimensions, spring properties, and strength

How to fit pins

Fitting pins correctly helps them hold securely and last longer:

• Prepare the hole - make sure the hole is the correct size, clean, and free of burrs. Add a small chamfer to the hole entrance to help the pin start straight
• Align the parts - line up the holes in all the parts the pin will pass through
• Use the right tool - use a pin punch, roll pin punch, or press. Roll pin punches have a small pilot tip that keeps the pin straight and prevents damage
• Drive the pin straight - tap or press the pin squarely into the hole, avoiding angled blows
• Position the slot - for slotted spring pins, avoid positioning the slot directly in line with the main load where possible
• Bend split pins correctly - after inserting a split pin, bend the legs apart and back around the bolt or pin so they cannot catch or slip out
• Use new split pins - split pins should not be reused, as bending weakens them

FAQ - All you need to know about pins

What is a spring pin?

A spring pin, also called a roll pin, is a hollow pin made from spring steel. When driven into a slightly smaller hole, it compresses and presses outwards against the hole, holding itself and the parts securely in place.

What is the difference between slotted and coiled spring pins?

Slotted spring pins have a single slot along their length, while coiled spring pins are rolled into a spiral. Coiled pins spread the load more evenly, absorb shock and vibration better, and often have better fatigue resistance.

What does DIN 1481 mean?

DIN 1481 is a standard for heavy duty slotted spring pins. It sets their dimensions, material, and performance, so pins made to this standard are consistent between suppliers.

What size hole do I need for a spring pin?

Spring pins are designed to fit into a hole matching their nominal diameter. The pin is made slightly oversize so it compresses when fitted. Check the manufacturer’s recommended hole size range for the exact pin.

What is the difference between a spring pin and a dowel pin?

A spring pin is hollow and flexible, holding itself in place by spring force. A dowel pin is solid and precisely sized, used to locate parts accurately in close-fitting holes.

What is a split pin used for?

A split pin is passed through a hole in a bolt, axle, or clevis pin, then its legs are bent apart to lock a nut or pin in place and stop it working loose.

Can I reuse spring pins and split pins?

Spring pins can sometimes be reused if they are undamaged and still grip firmly, but it is often best to fit new ones. Split pins should always be replaced, as bending weakens them.

How do I remove a spring pin?

Support the part, then use a pin punch slightly smaller than the pin to drive it out squarely from one side. A roll pin punch with a pilot tip helps stop the punch slipping.

Why choose stainless steel pins?

Stainless steel pins resist rust and corrosion, making them ideal for outdoor, marine, wet, and food-processing environments.

Why is my spring pin loose?

Common causes include a hole that is too large, a worn hole, the wrong pin size or duty, or a pin that has been reused and lost some of its spring force. Check the hole size and fit a new pin of the correct size.