• In Stock Items Ship in 24 Hrs
  • Save 5% on Orders over $100*
  • Exclusive Distributor Pricing
    • Set default Shopping List
    Your Shopping List is empty
    View List
    0
    Cart Total $0.00
    Items Total 0
    Web Discount $0.00

    Introduction to Woodruff Keys

    • Huyett Marketing Department
    •  05/06/2021
    • Updated 08/22/2024
    Woodruff Key Blog Hero Image
    Woodruff keys are essential components in mechanical engineering and are designed to secure gears, hubs, or other parts to a rotating shaft. Their semi-circular shape minimizes the risk of lateral movement by allowing them to sit deeper in the shaft. By acting as a fail-safe, these components protect costly components from the damage of shearing under excessive load.
    This guide explores the various aspects of woodruff keys, including their usage, installation, types, materials, and finishes. Additionally, it explains the unique sizing conventions of ANSI woodruff keys and highlights the advantages and potential drawbacks to help you select the right key for your application.
    Woodruff Machine Keys - Related Products
    ANSI WOODRUFF KEYS
    SEE PRODUCTS
    Woodruff Machine Keys - Related Products
    METRIC WOODRUFF KEYS
    SEE PRODUCTS
    Hi-Pro Keys - Related Products
    HI-PRO MACHINE KEYS
    SEE PRODUCTS

    What is a Woodruff Key?

    A woodruff key, also known as a half‑moon key, is a semi-circular machine shaft key that prevents gears, hubs, or other components from moving independently of a rotating shaft or spindle. These keys are inserted into a key seat created by a specific cutter or arbor cutter. A gear or other component with a woodruff keyway is then pressed onto the shaft until the key interfaces with its keyway.

    What is a Woodruff Key Used For?

    In addition to holding components in place on a shaft, woodruff keys also act as a fail-safe that protects expensive parts by shearing under excessive loads first. The crescent profile of the key allows it to sit deeper in the shaft, reducing the likelihood of the key rolling laterally out of the groove.

    How Does a Woodruff Key Work?

    When installed, the long, flat face of the woodruff shaft key protrudes above the host shaft. When a mating hub, gear, or other component is pressed onto the shaft, the protruding section of the key locks components together.
    Installed Woodruff Key

    How to Install a Woodruff Key:

    When installing a woodruff key into a keyseat, first press it into the half-moon groove which is milled into the shaft. Next, align the top flat portion of the key so that it is parallel with the host shaft before completing the connection.  
    During installation, the keys will sometimes slip out of their groove as the mating component is pressed on. This can make them difficult to install.

    How to Keep a Woodruff Key in Place

    To keep a woodruff key in place while installing a mating component, ensure that it is situated tightly in the key seat. Since these components are made to tight tolerances, they often require a press fit into their seat. This is done by lightly tapping the flat, protruding face of the key with a hammer or mallet until the key is seated firmly. The key will still extend above the mating shaft's surface and into the keyway to lock the mating hub or gear in place. If the key still falls or slips out during component installation, it is likely too small. 
    Woodruff Key Installation

    Selecting the Right Woodruff Key

    It is important to understand the different features of these keys during the design phase of an application. Some considerations include key type, material, and finish.

    What are the Different Types of Woodruff Keys?

    The two most common types are full-radius and flat-bottom woodruff keys. Both function the same but may be appropriate for different applications.
    It is important to note that flat-bottom keys are one of two variants of ANSI B17.2 woodruff keys; there are no flat-bottom metric key options. Additionally, both the flat-bottom and the full-radius designs are covered under the ANSI standard. It is up to the manufacturer’s discretion to produce either design (which may change per lot, regardless of the part number). This is why there is no attribute calling out the bottom type in specific product data.
    Woodruff Key Usage
    Full radius woodruff keys are a full half circle and make full contact with the shaft keyway. These keys require a precise keyseat, as contact can occur between the key and the bottom of the seat. This can cause interference and the key to protrude from the groove higher than desired.
    • Available in metric and ANSI B17.2 key options 
    Full Radius Woodruff Key Blog Image
    Flat bottom woodruff keys have the same profile as standard keys, except the bottom of the key has been shaved flat. The flat bottom reduces the potential of interference at the bottom of the seat, allowing the key to seat fully in the groove and alleviating potential clearance issues of excessive key height.
    • Available only in ANSI B17.2 key options 
    Flat Bottom Woodruff Key Blog Image
    Hi‑Pro keys, also known as high-profile woodruff keys, are a design variant that feature a full radius but have the added feature of feet. When installed, the feet extend over the face of the host shaft, preventing the key from rocking in its rounded seat.
    Hi-Pro Key Blog Image

    Woodruff Key Materials

    Woodruff keys are crafted in carbon steel, alloy steel, and stainless steel. Carbon steel woodruff keys and alloy steel woodruff keys are both durable, however they must be plated or coated to prevent corrosion. Stainless steel woodruff keys surpass carbon and alloy steel in corrosion resistance but are not as strong.

    Woodruff Key Finishes

    There are multiple finishes available for woodruff keys. Finishes include plain, clear and yellow zinc, and passivated.
    Plain finish is available on carbon steel and alloy steel woodruff keys. This finish is an economical solution for keys that will not be subjected to corrosive elements.
    Plain Finish Woodruff Key Blog Image
    Zinc plated woodruff keys  are plated in either yellow or clear zinc on carbon steel keys. The zinc plating offers an increased level of corrosion resistance compared to plain parts.
    Zinc Plated Woodruff Key Blog Image
    Passivated finish woodruff keys use an oxidation process suitable for stainless steel parts. This microfilm is added to provide additional corrosion resistance to the already resilient material.
    Passivated Finish Woodruff Key Blog Image

    Product Considerations

    As with any fastener, there are advantages and disadvantages to using these keys. Carefully consider the following lists to help you determine which fastener will fulfill your application requirements: 

    Advantages of a Woodruff Key Include:

    • Adjusts to any taper present in mating piece or shaft
    • Ideal for high speed rotating assemblies
    • Eliminates milling near shaft shoulders reducing stress concentrations at the shaft end
    • Deeper seat in the shaft reduces risk of rolling out of key seat
    • Provides a more exact fit, reducing play in the key seat
    • Easy removal

    Some Disadvantages to Consider Are:

    • Deeper groove depth weakens strength of shaft
    • Can rock during assembly making it difficult to install
    • Carries less load compared to longer machine keys
    • Key seat requires machining with special cutting tools

    How are Woodruff Key Sizes Measured?

    Woodruff keys often can be confusing to measure, especially ANSI keys. Use the table below to learn which measurements are required to select the correct sizes for metric, inch, and hi-pro options.
    Download the How to Measure Woodruff Keys quick guide here:
    How to Measure Woodruff Keys Thumbnail
    How to Measure Woodruff Keys
    Metric Woodruff Keys
    • Width (A) - Overall thickness of the machine key.
    • Diameter (B) - The full circle diameter of the machine key. This often creates confusion since the full circle diameter cannot be measured directly. Overall length (F) of the woodruff key will always be less than full circle diameter.
    • Height (C) - Height is measured from the lowest point of the key to the flat top face.
    • Key Length (F) - Length is the end to end measurement of the flat top face of the key where it protrudes above the mating shaft.
    • Key Length (F) - Length is the end to end measurement of the flat top face of the key where it protrudes above the mating shaft.
    		Metric Woodruff Key Diagram
    ANSI Woodruff Keys - Full Radius & Flat Bottom*
    • Width (A) - Overall thickness of the machine key.
    • Nominal Diameter (B) - The full circle diameter of the machine key. This often creates confusion since the full circle diameter cannot be measured directly. Overall length (F) of the woodruff key will always be less than full circle diameter.
    • Height (C) - Distance is measured from the lowest point of the key to the flat top face.
    • Length (F) - Length is the end to end measurement of the flat top face of the key where it protrudes above the mating shaft.
    		ANSI B17.2 Woodruff Keys Diagram
    Hi-Pro Keys - Full Radius & Flat Bottom*
    • Width (A) - Overall thickness of the machine key.
    • Nominal Diameter (B) - The full circle diameter of the machine key. This often creates confusion since the full circle diameter cannot be measured directly.
    • Height (C) - Distance is measured from the lowest point of the key to the flat top face.
    • Length (F) - Length is the end to end measurement of the flat top face of the key where it protrudes above the mating shaft.
    • Lip Height (G) - Overall height of the lip.
    		Hi-Pro Key Diagram
    *For Inch and Hi-Pro Woodruff Keys, both flat and radius bottom styles are standard designs produced and shipped at the manufacturer's discretion. If a specific style is required, please give us a call at 785-392-3017.

    How to Read an ANSI Woodruff Key Number

    A key number only applies to those keys covered by the ANSI B17.2 standard, not to metric or other keys. On those covered by ANSI B17.2, the number conveys the key’s outside diameter (OD) with the last two digits and the nominal width with all preceding numbers.
    More specifically, the OD is expressed in 8 th in. increments, while the width is expressed in 32 nd in. increments.
    For example:
    This M4 x 5 carbon steel woodruff key has the key number 808.
    • 8_ _ = 8/32in. width (simplified to 1/4in.)
    • _08 = 8/8in. OD (simplified to 1in.)
    The number 808 communicates the 1/4in. width x 1in. OD in the product title.
    808 Woodruff Key Example
    This should not be confused with the product’s Huyett part number, which in this case is WKC-015. The 808 key number is designated by ANSI, which has nothing to do with the 015 Huyett part number . 
    Fortunately, there is no such confusion with metric keys. The product description lists the width x height as measured (ex.: a M4 x 5 carbon steel woodruff key features a 4.00mm. width and a 5.00mm. height).

    ANSI Woodruff Key Size Chart with Numbers

    The table below lists Huyett’s selection of ANSI keys as they relate to their ANSI number.
    Download the full chart with icons featuring real sizing dimensions here:
    *The downloadable chart pictures icons sized to the real key dimensions; simply lay your key on the chart until you find the correct size. You MUST print the chart in portrait orientation to size on 8.5 x 11in. paper to keep dimensions accurate.
    ANSI B17.2 Woodruff Keys Chart Thumbnail
    PREFIX OPTIONS:
    WKC = Carbon Steel, Plain
    WKS = Stainless Steel, Plain
    WKA  = Alloy Steel, Plain
    ###-ZC  = Zinc Clear
    ###-ZY  = Zinc Yellow
    ANSI B17.2 Woodruff Keys Diagram
    Pair prefixes with Huyett part numbers:
    Ex: WKC-061-ZC = Carbon steel ANSI 605 key with zinc clear finishing
    Woodruff Key Dimensions
    A: Width
    B: Nominal Diameter
    C: Height
    D: Optional Flat Bottom Height*
    F: Overall Length
    *Optional flat bottom height is implemented at the manufacturer's discretion.
    Shaded Nominal Length Boxes* = Key numbers with a "-1" have a shorter length than those with the same preceding number.
    ANSI  KEY NUMBER
    NOMINAL DIAMETER
    OVERALL LENGTH
    NOMINAL WIDTH
    WIDTH
    HUYETT PART NUMBER
    (no prefix)
    1/4
    0.248
    1/16
    0.0625
    5/16
    0.311
    1/16
    0.0625
    3/32
    0.0937
    3/8
    0.374
    1/16
    0.0625
    3/32
    0.0937
    1/8
    0.1250
    1/2
    0.491
    1/16
    0.0625
    3/32
    0.0937
    1/8
    0.1250
    5/8
    0.612
    3/32
    0.0937
    1/8
    0.1250
    5/32
    0.1562
    3/16
    0.1875
    3/4
    0.740
    1/8
    0.1250
    5/32
    0.1562
    3/16
    0.1875
    1/4
    0.2500
    7/8
    0.866
    5/32
    0.1562
    3/16
    0.1875
    7/32
    0.2187
    1/4
    0.2500
    1
    0.992
    3/16
    0.1875
    7/32
    0.2187
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    1 1/8
    1.114
    3/16
    0.1875
    7/32
    0.2187
    1/4
    0.2500
    5/16
    0.3125
    1 1/4
    1.240
    3/16
    0.1875
    7/32
    0.2187
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    1 3/8
    1.362
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    1 1/2
    1.484
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    2 1/8
    1.723
    3/16
    0.1875
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    2 1/8
    1.380*
    3/16
    0.1875
    Body Cell
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    2 3/4
    2.317
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    7/16
    0.4375
    1/2
    0.5000
    2 3/4
    2.000*
    1/4
    0.2500
    5/16
    0.3125
    3/8
    0.3750
    7/16
    0.4375
    1/2
    0.5000
    3 1/2
    2.880
    3/8
    0.3750
    1/2
    0.5000
    5/8
    0.6250
    3/4
    0.7500

    Metric Woodruff Key Size Chart

    The table below lists Huyett’s selection of metric woodruff keys.
    All Huyett metric woodruff keys are in accordance with DIN 6888.
    Download the full chart with icons featuring real sizing dimensions here:  
    *The downloadable chart pictures icons sized to the real key dimensions; simply lay your key on the chart until you find the correct size. You MUST print the chart in portrait orientation to size on 8.5 x 11in. paper to keep dimensions accurate.
    Metric Woodruff Key Size Chart Thumbnail
    PREFIX OPTIONS:
    WKMX-XXXXXX = Carbon Steel, Plain
    WKMC-XXXXXX-ZY = Zinc Yellow Finish
    WKMC-XXXXXX-ZC = Zinc Clear Finish
    Metric Woodruff Key Size Chart Diagram
    * Any measurements with max./min. options are sized to the max. option.
    Metric Woodruff Key Dimensions
    A: Width
    B:  Diameter
    C: Height
    F: Key Length
    7.0 mm
    2.50 mm
    2.60 mm
    1.475 mm
    1.50 mm
    1.975 mm
    2.00 mm
    10.0 mm
    3.58 mm
    3.70 mm
    1.975 mm
    2.00 mm
    1.975 mm
    2.00 mm
    2.475 mm
    2.50 mm
    2.975 mm
    3.00 mm
    2.975 mm
    3.00 mm
    13.0 mm
    4.88 mm
    5.00 mm
    1.975 mm
    2.00 mm
    2.975 mm
    3.00 mm
    2.975 mm
    3.00 mm
    3.970 mm
    4.00 mm
    3.970 mm
    4.00 mm
    16.0 mm
    6.35 mm
    6.50 mm
    2.975 mm
    3.00 mm
    3.970 mm
    4.00 mm
    3.970 mm
    4.00 mm
    4.970 mm
    5.00 mm
    4.970 mm
    5.00 mm
    19.0 mm
    7.35 mm
    7.50 mm
    3.970 mm
    4.00 mm
    4.970 mm
    5.00 mm
    4.970 mm
    5.00 mm
    5.970 mm
    6.00 mm
    5.970 mm
    6.00 mm
    22.0 mm
    8.85 mm
    9.00 mm
    4.970 mm
    5.00 mm
    4.970 mm
    5.00 mm
    5.970 mm
    6.00 mm
    5.970 mm
    6.00 mm
    7.964 mm
    8.00 mm
    25.0 mm
    9.85 mm
    10.00 mm
    4.970 mm
    5.00 mm
    5.970 mm
    6.00 mm
    6.964 mm
    7.00 mm
    28.0 mm
    10.82 mm
    11.00 mm
    5.970 mm
    6.00 mm
    5.970 mm
    6.00 mm
    7.964 mm
    8.00 mm
    7.964 mm
    8.00 mm
    9.964 mm
    10.00 mm
    32.0 mm
    12.82 mm
    13.00 mm
    7.964 mm
    8.00 mm
    7.964 mm
    8.00 mm
    9.964 mm
    10.00 mm
    45.0 mm
    15.82 mm
    16.00 mm
    9.964 mm
    10.00 mm

    Looking For More?

    For additional information, visit our blog page as well as the Key Stock and Machine Keys FAQ. If you don't see what you are looking for, our experienced and friendly Sales team is ready to help. 

    Catalogs & Resources

    We have the most comprehensive catalogs of hard-to-find, hard-to-make, and hard-to-buy parts on the planet – all under one roof.

    Find What You Need

    Catalogs And Resources Block