Key Stock Material Selection Guide

Huyett Marketing Department
10/10/2019
Updated: 04/13/2023

Key stock is an important – and perhaps one of the most popular – element of the fastener world. It is used on its own or as the starting point to make other fasteners, particularly in
power transmission applications. But what exactly is key stock, and what type of material is it made from?

What is Key Stock?

Key stock
is a term that generally refers to
square or
rectangular cold-drawn metal bars that are at least one foot in length and often manufactured to specific tolerances. Other shapes – like
hex,
round, and
step – are available. Key stock should not be confused with machine keys (although the terms are used interchangeably). Machine keys are smaller components cut from key stock.

There are several
fastener industry standards that regulate key stock dimensions, although standard conformance is not necessary. In many cases, if your application requires precision tolerances (whether they must comply with a standard or not), Huyett’s
in-house manufacturing capabilities allows us to cut and/or mill your key stock down to your desired measurements.

However, we do offer key stock that is prefabricated to ANSI B17.1 and several ASTM and DIN standards.

How is Key Stock Used?

Key stock is a versatile product with several uses, both in manufacturing and in the field. In manufacturing, key stock is used to create machine keys as an end product.
Machine keys – also known as shaft keys – are essential components in a power transmission application that transmit torque from a rotating shaft to the attached gear. They are used as a “first defense” because they are designed to be the first thing to break, thus preserving the more expensive components in the application.

In the field, key stock is kept on hand to replace broken machine keys on site or for general maintenance.

What is Key Stock Material?

Key stock (and machine keys) can be made from many types of materials. Typically, key stock is made from metals like carbon steel or stainless steel, aluminum, brass, copper, and Monel®. Each type of key stock metal includes varying material grades that offer different benefits based on their properties.

Metal Properties

There are many properties (characteristics) that metal exhibits to communicate how well it will hold up in a given application. To truly understand a metal’s functionality, it is important to clarify a few basic terms.

Strength:
A metal’s ability to resist being permanently pulled or bent
Workability:
A metal’s ability to be squeezed, stretched, bent, or connected in both its hot and cold forms
Machinability:
A metal’s ability to be cut
Hardenability:
A metal’s ability to hold its shape and structure under a compressive force
Corrosion Resistance:
A metal’s resistance to natural and manmade corrosive elements

For a more in-depth review of these and other properties, read Huyett’s
Introduction to Mechanical Properties of Metals.

Types of Key Stock Material

While key stock comes in many different materials, it is mostly available in varying types of steel, aluminum, and brass. Other materials – like Monel™ and even nylon – are options but are not as common as the main metals. Here, we delve into the different types of key stock material that Huyett offers.

Steel

Steel encompasses a broad range of materials including carbon steel, stainless steel, and alloy steel (each of which are detailed in Huyett’s
Engineering Handbook). While carbon is present in all steel, each steel family has a different combination of alloys (additional metals that add to or enhance the primary metal).

Carbon Steel

Carbon steel, often referred to as plain carbon steel, is a popular choice for key stock, partially because it is an economical choice. It is also good for a wide range of applications in industrial, construction, and automotive industries.

The point of adding carbon to steel is to increase its strength. It does not take much; in fact, the last two digits in steel grade classifications reference the fractional percentage of carbon present in that grade.

For example, 1018 carbon steel tells us that this grade only contains 0.18% carbon. Most steel contains less than 2% carbon; any more gets into the “cast iron” family, where metal is much more brittle. The first two digits refer to the alloy group the metal belongs to; in the 1018 example, 10 refers to plain carbon steel.

Here are three of the most common carbon steel key stock grades:

1018 Carbon Steel

Strength:
Strong, but the least strong of the three grades due to low carbon
Corrosion Resistance:
Does not resist rust and oxygen exposure well
Hardness:
The least hard of the three grades
Workability:
Excellent for welding and cold forming
Other Information:
The most common rolled steel
Applications:
Shaft pins, rods, sprockets, clevis pins, and machine keys

1045 Carbon Steel

Strength:
Stronger than 1018
Corrosion Resistance:
Similar to 1018
Hardness:
Harder than 1018
Workability:
Less workable than 1018, but not impossible
Other Information:
Resistant to wear
Applications:
Similar to 1018

1095 Carbon Steel

Strength:
Strongest of the three grades
Corrosion Resistance:
Similar to 1018
Hardness:
Hardest of the three grades
Workability:
High carbon content makes this very difficult to work
Other Information:
Common choice for cutlery because of its hardness
Applications:
Great for applications that require sharp edges and wear resistance

Stainless Steel

Stainless steel’s main elements are iron and chromium. The latter makes the steel “stainless” (highly resistant to rust). From here, stainless steel branches out into five different categories, each with unique alloying properties and designated by a “100 series” classification system:

Austenitic:
200 & 300 series – Corrosion resistant and durable in a wide range of temperatures
Martensitic:
400 series – Magnetic, hard, and good for sharp applications like knives
Ferritic:
400 series – Magnetic, economical, and good for decorative applications
Duplex:
A mix of ferrite and austenite
Precipitation-Hardening:
Heat treatable, magnetic, and corrosion resistant

Some of the most versatile grades of stainless steel are:

303 Stainless Steel

Strength:
Good, but not as strong as 304
Corrosion Resistance:
Decent, but not designed to withstand extreme natural elements
Hardness:
Not as hard as 304
Workability:
Additional sulfur makes 303 extremely machinable, but not very weldable
Other Information:
One of the most workable stainless steels available
Applications:
Good for small fasteners and applications requiring machinability

304 Stainless Steel

Strength:
Decent strength, but not as much as 316
Corrosion Resistance:
Good resistance to natural elements and chemicals
Hardness:
Middle-of-the-road hardness for stainless steel
Workability:
Great for welding and machining
Other Information:
Economical; considered the most versatile stainless steel available
Applications:
Used widely, but particularly in the food industry

316 Stainless Steel

Strength:
Addition of molybdenum makes it slightly stronger than 304
Corrosion Resistance:
Excellent resistance to extreme environments, including saltwater and sub-zero temperatures
Hardness:
Similar to but slightly harder than 304
Workability:
Good machinability and excellent weldability
Other Information:
Known as the marine grade; more expensive than 304, but much better corrosion resistance
Applications:
Good for a wide range of applications, including lab equipment, saltwater applications, and medical equipment

410 Stainless Steel

Strength:
Known for its high strength as a martensitic stainless steel
Corrosion Resistance:
Good resistance to mild natural elements, foods, and acids
Hardness:
High
Workability:
Good for welding and easy to machine if it is annealed or tempered
Other Information:
Economical choice
Applications:
Good for knife blades, fasteners, and spring pins

416 Stainless Steel

Strength:
Decent, but can be increased with heat treatment
Corrosion Resistance:
Good resistance to mild natural elements and food acids
Hardness:
Variable, depending on if it is tempered or hardened
Workability:
Most machinable stainless steel available
Other Information:
Economical choice
Applications:
Good for fasteners, washing machines, and applications with high machining needs

Alloy Steel

Alloy steels still contain carbon, but also consist of about 5% alloying elements including manganese, molybdenum, chromium, vanadium, nickel, and tungsten. Similar to the plain carbon steel classification, alloy steels’ four-digit names signify their alloy groups and their fractional percentage of carbon. Two of the most common alloy steel grades are:

4140 Alloy Steel

Strength:
The addition of molybdenum gives it a higher strength than carbon steel
Corrosion Resistance:
Added chromium elevates its resistance to natural elements
Hardness:
Better hardness than carbon steel
Workability:
Highly forgeable, but less cold-workable or weldable than 1018
Other Information:
Used for military clevis pins
Applications:
Extremely versatile and used widely in most industries, including aerospace

8630 Alloy Steel

Strength:
Includes molybdenum and nickel, making it stronger than 4140
Corrosion Resistance:
Similar to 4140
Hardness:
Good hardenability
Workability:
Good ductility, weldability, and machinability
Other Information:
Economical substitute for more expensive alloy steels
Applications:
Key stock, machine keys, and automotive parts

Importance of High Strength Steel

Key stock can be made from steels that possess different strengths. Most carbon and some types of stainless steels can have their strengths increased through heat treatment. A designer must know the calculated or actual strength of the key stock to ensure that it will withstand the operating pressures applied in service. A material that does not have enough strength to withstand the operating pressures will fail.

Aluminum

Aluminum alloys are roughly one-third the weight of steel but have great relative strength. They rival steel in corrosion resistance and heat conductivity and are used in many industries that need light frames, like the aerospace industry.

Similar to the carbon steel classification system, aluminum’s four-digit name indicates main alloys, natural or controlled impurities, and trace alloys. In Aluminum 6061, one of the most common grades, 6 indicates that the main alloys are silicon and magnesium, 0 indicates natural impurities, and 61 indicates that there are several trace alloys, including chromium and copper.

Common aluminum alloys include:

6061 Aluminum

Strength:
Decent strength; not as strong as 1018 carbon steel
Corrosion Resistance:
Good resistance to atmospheric conditions; exceptional resistance to ammonia, ammonium hydroxide, and nitric acid
Hardness:
Not as hard as steel
Workability:
Good for forming and welding
Other Information:
Good for electrical conductivity
Applications:
Great general-use aluminum; widely used in architecture and structural applications

4140 Aluminum

Strength:
Good with aluminum expectations
Corrosion Resistance:
Resistant to basic natural elements but can be susceptible because of its copper content
Hardness:
Decent
Workability:
Good for forming and welding
Other Information:
Conducts heat better than steel
Applications:
Good for a wide range of applications, including framework structures, electronic parts, and airplanes

Brass

Brass is a subcategory of copper, which is a pure metal. Brass contains mainly copper and zinc in a roughly 60/40 split. Like most metals, alloys are added to create different grades.

In comparison to steel, while brass is not typically as strong, it is generally more machinable, more corrosion resistant, and more conductive of heat.

You will see the name for a brass grade in a few different forms, most likely as three and five digits. The industry traditionally gave brass grades arbitrary three-digit names, and the United Number System (UNS) adopted those names and added two digits to create alloy groups:

20000-29999:
Copper/Zinc Alloy
– Zinc contributes to strength (brass with over 40% zinc will start to lose malleability)
30000-39999:
Copper/Zinc/Lead Alloy
– Lead increases machinability
40000-49999:
Copper/Zinc/Tin Alloy
– Tin increases corrosion resistance in saltwater

The numbers are only organizational and do not communicate any percentage of alloys.

360 and 464 are two of the most popular brass grades:

360 (36000) Brass

Strength:
Contains roughly 35% zinc; high strength, but still workable
Corrosion Resistance:
Good resistance to natural elements and coolant
Hardness:
High
Workability:
Lead contributes to high machinability
Applications:
Well suited for heavy industry use, including plumbing, and applications that require high machinability

464 (46400) Brass

Strength:
Contains roughly 40% zinc; very high strength brass
Corrosion Resistance:
High, especially in saltwater
Hardness:
High
Workability:
Forgeable and heat workable
Other Information:
Known as “naval brass” for its use in marine environments
Applications:
Good for marine applications, bushings and turnbuckles, and decorative applications

Monel®

Monel® is a registered trademarked name for a particular group of nickel alloys. They are composed of mostly nickel and copper, with each grade including other trace elements. While its workability is not nearly that of steel, the alloy class displays high corrosion and heat resistance.

400 Monel®

Strength:
High
Corrosion Resistance:
High, especially against saltwater and sulfuric and hydrofluoric acid
Hardness:
Hardens during cold working
Workability:
Fair, but requires specific forging and welding techniques
Other Information:
Keeps its corrosion and strength properties at over 700°F
Applications:
Great for marine applications, chemical environments, and extreme temperatures

Key Stock Metal Tolerance: Moltrup®

Moltrup® can be a confusing term. It does not refer to a specific type of material; instead, it references a tolerance quality introduced by the Moltrup Steel Products Co. in Pennsylvania. This tolerance meets the ASME B17.1 Class 2 fit, which is a tight key stock and key seat fit.

1018, 1045, and 8630 steel grades are some of the metals that can conform to the Moltrup quality.

Other Key Stock Material: Nylon

In addition to metal, nylon key stock is also available. While it is not nearly as strong as steel, it is cost efficient, flexible, durable, and resistant to chemicals.

Nylon comes in several grades, but 6/6 offers a range of characteristics that make it a good choice for key stock:

6/6 Nylon

Strength:
About 1/10th the strength of low carbon steel
Corrosion Resistance:
Good resistance to oil, gas, and chemicals
Hardness:
Good
Workability:
High
Other Information:
Electrically insulating
Applications:
Can be an economical substitute for metal washers and bearings and is used widely in many industries, particularly the medical industry

Choosing the Right Key Stock Material

Key stock materials should be chosen based on the operating environment. You should carefully consider the loads that will be applied to the material and what type of atmosphere it will be subjected to in service.

Carbon steel provides very good strength and can be altered through heat treatment to provide a higher degree of strength or wear resistance. Alternatively, austenitic (300 series) stainless steel key stock material should be used where the material will be exposed to highly corrosive environments, and martensitic stainless-steel key stock material should be used when higher strength material is required and exposed to mildly corrosive environments.

Where brass is concerned, lead alloys offer high machinability and are often used in plumbing, where tin alloys are good options for marine applications. Nickel alloys offer corrosion resistance to extreme elements, and nylon is well suited for economical applications that require resistance to chemicals.

In addition to operating environments, you should consider cost and availability when choosing key stock material. One of the many
benefits of becoming a Huyett distributor is having your material’s real-time price and stock status immediately available at your fingertips through our online experience.

Should I Add Finish to My Key Stock?

Adding key stock finish is something to consider depending on the type of elements that the material will exposed to, as many finishes increase corrosion resistance, hardenability, and aesthetic appeal. Specific finishes, like phosphate conversion coatings, also absorb liquids and improves adhesion. Others, like nickel electroplating, improve the material’s conductivity.

The designer should carefully consider the role of the material and if finishes would enhance its performance. For a more in-depth look at available material finishes, check out Huyett’s
Metal Finishes Introduction.

The Bottom Line

Key stock is widely used to make
machine keys for power transmission applications. Since they are used to protect the expensive components within the application, it is important to understand what key stock material is available and how to choose the right one.

Huyett stocks hex, rectangle, round, square, and step key stock in multiple materials with a variety of optional finishes. To learn more about our options, browse our
Key Stock catalog or
our key stock selection, or
contact our Sales Team for more information.