There are a variety of hardware options for different sheet metal fabricated parts. Choosing the best ones for your project should be considered during the design and take into consideration the type, the material, tolerance, and placement.
Common fastener hardware includes bolts and nuts, screws, and rivets – which all come in a variety of types, sizes, and materials.
1) Is the joint permanent or will you be taking it apart for maintenance or repairs?
2) Will the joint be exposed to vibration?
3) What strength requirements do you have for the fastener?
4) Is it possible to bring all components to an assembly machine?
5) Can you access the back of the joint?
6) How much backup space is available?
7) How hard is the part material?
8) How thin is the part material?
9) What special fastener features are important for the joint that might limit your options?
10) What is the best option with respect to cost?
Rivets are common, permanent fasteners which are used in both small and large applications.
A rivet includes a head and a tail – which is beaten out or compressed once in place.
Common types of rivets include:
Screws are generally high strength fasteners which can be removed if repair or maintenance is necessary.
Bolts require a nut or pre-tapped hole to form a joint. Washers are used to help spread the load over a larger area.
Galvanic corrosion is always an important consideration when designing sheet metal parts with hardware.
Issues arise when two dissimilar metals are in physical or electrical contact in an electrolyte solution.
Under these circumstances, one of the metals can corrode more rapidly than expected.
To avoid issues, whenever possible choose the same metal for fasteners as you have for the part.
When that is not possible, choose metals close to each other on the galvanic table and take actions to eliminate the physical or electrical contact between the part and the hardware.
This can be done with coating and non-conductive barriers. It’s also possible to use a sacrificial anode to prevent galvanic corrosion.
Please read this article to get a better understanding of galvanic corrosion and how to prevent it.
Best practices to avoid galvanic corrosion for hardware includes:
This table can be used to help with your selection of fastener and part materials
|Base Metal||Fastener Metal|
|Zinc, galvanized steel||Aluminum and aluminum alloys||Steel and cast iron||Brasses, copper, bronzes, monel||Stainless steel type 410||Stainless steel type 302/304, 303, 305|
|Zinc, galvanized steel||A||B||B||C||C||C|
|Aluminum and aluminum alloys||A||A||B||C||Not recommended||B|
|Steel and cast iron||AD||A||A||C||C||B|
|Teme (lead tin) plated steel||ADE||AE||AE||C||C||B|
|Brasses, copper, bronzes, monel||ADE||AE||AE||A||A||B|
|Stainless steel type 430||ADE||AE||AE||A||A||A|
|Stainless steel type 302/304||ADE||AE||AE||AE||A||A|
A: Corrosion of the base metal is not increased by the fastener
B: Corrosion of the base metal is marginally increased by the fastener
C: Corrosion of the base metal may be marginally increased by the fastener material
D: Plating on the fasteners is rapidly consumed, leaving the bare fastener metal
E: Corrosion of the fastener is increased by the base metal
In another article we discuss the importance of understanding tolerances when designing sheet metal parts for fabrication.
Tolerances help you understand minimum requirements for placement of hardware and fasteners.
Always confirm tolerances and placement requirements with your custom fabricator so your design meets their requirements.
The table below is provided as a guideline but can vary based on the material you’re using, the fabricator’s equipment and tools, and other factors.
They may need to be adjusted for each project so your fabricator should be an important partner in your design stages.
Tolerances Guideline for Hardware in Sheet Metal Fabrication
|Hole to hardware||±0.254 mm (0.010″)|
|Edge to hardware||±0.254 mm (0.010″)|
|Hardware to hardware||±0.0381 mm (0.015″)|
|Bend to hardware||±0.0381 mm (0.015″)|
*Please use these numbers as guidelines only and always check with your fabricator for their recommendations before completing your design.
The PennEngineering website provides additional details and specifications for common fasteners.
Stainless steel, steel, silicon bronze, brass, and aluminum are common materials used for manufacturing fasteners.
Coatings using zinc, chrome, or hot dip galvanization are also used.
|Stainless steel fasteners||· Good corrosion resistance even if damaged or scratched||· Not as strong as hardened steel fasteners|
· Susceptible to seizing during installation
|Steel fasteners||· Most common material used for fasteners|
· Can be used with or without surface coatings. Common coatings include galvanization, zinc or chrome plating
· Galvanization improves corrosion resistance
|· Uncoated steel will corrode|
· Different grades are available with different hardness and strengths so its important to know which one you should use
|Silicon bronze fasteners||· Very good corrosion resistance|
· Primarily used in marine or saltwater environments
· Stronger than brass
· Sometimes used for aesthetic purposes
|· High cost|
|Brass fasteners||· High corrosion resistance|
· Electrically conductive
· Used mostly for its aesthetic properties
|· Softer than other options|
|Aluminum fasteners||· Good corrosion resistance|
· Remains corrosion resistant even if damaged or scratched
· Aluminum alloys are common (manganese, silicon, iron, magnesium, zinc, copper)
|· Softer than other options|
|Zinc plated fasteners||· Improved corrosion resistance|
· Appearance is shiny with a silvery or gold colour
|· Steel coated with zinc will rust if the zinc plating is damaged|
|Chrome plated fasteners||· Improved corrosion resistance|
· Finish is shiny and polished
|· Steel coated with chrome will rust if the plating is damaged|
· High cost
|Hot dip galvanized fasteners||· Applies a thicker coating of zinc than zinc plating providing better corrosion resistance|
· Commonly used in outdoor and marine environments
|· Hot dipped galvanized bolts are not compatible with any nuts other than hot dipped galvanized ones.|
· Hot dipped galvanized nuts are tapped differently because of the thickness of the coating.
Read more about designing for sheet metal fabrication: