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Compression Limiters

Metal Compression Limiters provide and maintain bolted joint integrity of a plastic assembly. Compression Limiters are designed to protect the plastic components of an assembly from the compressive loads generated when a bolt is tightened to its recommended tightening torque, thereby assuring that the joint remains intact throughout the life of the product.

SPIROL offers a range of both formed and machined Compression Limiters including split seam, molded in, oval and solid wall designs. Each type of Compression Limiter is designed to accommodate different compressive loads, positional tolerances and installation methods. All formed Compression Limiters, except the Series CL220, are zinc plated and have a supplementary coating of trivalent passivation and an organic sealant for corrosion resistance. This finish provides 144 hours to white corrosion, and 384 hours to red corrosion when salt spray tested in accordance with ASTM B117. SPIROL’s Series CL220 Compression Limiters are coated with ArmorGalv®, a zinc alloy thermal diffusion coating that provides a minimum of 1000 hours corrosion resistance to red rust. Machined Limiters are manufactured from aluminum and brass, both of which have inherent corrosion resistant properties and thus do not require supplementary finishing.

The clearance between the bolt and the inside diameter of the installed Compression Limiter is adequate to meet normal misalignment. The Compression Limiter’s length should be designed to ensure it will bottom out against the surface under the bolt’s head and mating component. The appropriate length and length tolerance is application dependent. While the standard tolerance is sufficient to meet most needs, verification is recommended. SPIROL‘s Applications Engineers are available to assist in this process. If it is determined that a special Compression Limiter is required, then a documented recommendation will be provided.

It is imperative that the proper Compression Limiter be designed into each application based on the specific requirements for that assembly, and that the plastic host be designed appropriately to ensure that bolted joint integrity is maintained throughout the life of the assembly. SPIROL’s Application Engineers are available to work with you to determine the most appropriate Compression Limiter for your application.

Compression Limiter Types

SPIROL offers a comprehensive line of split seam, molded in, oval and solid wall designs to accommodate different compressive loads, positional tolerances and installation methods for bolts ranging in size from M3 to M12 and #4 to 3/8” - depending on the type of Compression Limiter. For simplicity, SPIROL has broken down the different types by the two different installation methods below: Post Mold Installed Compression Limiters and Molded-In Compression Limiters. Some series of Compression Limiters can be either pressed in or molded in, while others can only be installed by one method.

If one of SPIROL's standard Compression Limiters does not meet your needs, our Application Engineers will work with you to design a custom Compression Limiter to meet your unique requirements. Select from the options below for more specificity about SPIROL's Compression Limiter offering or contact us for complimentary technical support!

Standard Offering Breakdown & Materials



CL220 M4 - M12 Press-In B - High Carbon Steel UNS G10700 / G10740
CS67S (1.1231) / CS75S (1.1248)
8.8 5 Radial Tension / ArmorGalv®
CL200 M4 - M8 Press-In 8.8 5 Radial Tension / Reduced Profile
CL350 M6 - M8 Press-In 10.9 8 Radial Tension / Heavy Wall
CL400 M6 - M8 Press-In 8.8 5 Radial Tension / Oval
CL460 M6 - M8 Mold-In 8.8 5 Radial Groove / Oval
CL500 M6 - M8 /
#10 - 5/16
Mold-In F- Low Carbon Steel UNS G10060 / G10100
EN10139 DC04 (1.0338) / DC01 (1.0330)
8.8 5 Radial Groove / Round
CL6000 M3 - M10 Either Press-In or Mold-In
A - Aluminum ASTM B211 2024
ISO AlCu4Mg1
Knurled / Solid Wall / Lightweight / Lead Free
CL6100 CL6000 w/ Head 
CL8000 E - Brass UNS C36000
EN 12164 CW603N CuZn36Pb3
Knurled / Solid Wall / Cathodic Alt. to Aluminum
CL8100 CL8000 w/ Head
CL620 M3 - M8 A - Aluminum ASTM B211 2024
ISO AlCu4Mg1
Knurled / Solid Wall / Lightweight / Lead Free

Don’t See What You’re Looking For?

Need help choosing the most appropriate fastening solution for your application? SPIROL's Application Engineers will review your specific requirements, and design the most cost-effective Compression Limiter to meet your technical and commercial needs. Let us help!

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Determination of Compression Limiter Length

Proper length specifications of both the Compression Limiter and the plastic component are crucial to the proper performance of the bolted joint. The recommended maximum length of the Compression Limiter is the minimum thickness of the plastic component. This assures that when the proper load is applied to the bolt two critical conditions will be met:

  • The bolt will be in contact with the Compression Limiter, eliminating the possibility of creep.
  • The plastic host will always have a small amount of compression applied.

The amount of compression on the plastic host will be at most the combined thickness and length tolerances of the two components and the amount of compressive deflection on the Compression Limiter. In reality, with good SPC and production controls, the actual compression will be much less.

Load Rating

SPIROL rates our Compression Limiters by matching the load required to compress the Limiter 2.5% of its nominal length to the clamp load of the nominal sized fastener. See Table.

Compression Limiters are rated by the load required to compress the Limiter to a defined, safe distance that meets the requirements of:

  • Maintaining integrity of the Compression Limiter, preventing rupturing or excessive swelling.
  • Maintaining the integrity of the plastic host by keeping any localized compressive strains within generally accepted, safe limits.
  • Maintaining the load of the fastener by preventing stress relaxation, thereby assuring the continued integrity of the bolted connection.

For all engineered thermoplastic materials used in durable manufactured products, allowing 3%-5% maximum compression has been determined to be a safe, conservative limit. Most plastics are perfectly safe being compressed 5%-7%; many even further. Plastics have the characteristic that they will very quickly exhibit stress relaxation in the areas of high compression eliminating the potential of stress cracking and allowing the Compression Limiter to take the fastener load.

Compression Limiter Series
Bolt Rating
Class Grade
CL200 / CL220 8.8 5
CL350 10.9
CL400 8.8
CL460 8.8
CL500 8.8 5
CL6000 / CL6100 10.9 8
CL8000 / CL8100 10.9 8
CL620 10.9 8

Critical Design Guidelines

The following design guidelines should be considered when a Compression Limiter is used to ensure its effectiveness in the plastic assembly:

  1. Bolt is tightened to 75% of its proof load.
  2. Bolt head applies a clamp load on the plastic and bottoms out on the Limiter.
  3. Host thickness is greater than or equal to the length of the Limiter, and able to absorb the clamp load.
  4. The installed Limiter is aligned with the Insert (when used) to prevent a jack-out condition.
  5. Plastic compression ~ 3% - 5%.
  6. Limiter is compressed between bolt’s head and mating component.
  7. Correct hole size ensures retention of the Limiter.
  8. The mating component can withstand compression force generated by bolt.
Ideal Bolted joint

Machined or Formed Compression Limiters?

How does a designer choose between machined or formed Compression Limiters? Formed steel is often the most economical option. However, for short Compression Limiters, particularly when the length to diameter ratio is less than 1, it makes most sense to use a Machined Limiter because it difficult to form a Limiter with a short length and maintain square ends.

Below are guidelines as to how to choose between Machined or Formed Compression Limiters:


  • Best option for short Compression Limiters (L:D ≤ 1)
  • Great for plastics with very low viscosity when molding-in
  • Can be supplied with a head for larger bearing surface for soft mating materials; head eliminates washer (but you could use a flange bolt instead)
  • Can be molded-in or pressed into assembly
  • Aluminum is lightweight and lead free (and stronger than brass)


  • Less expensive
  • Can be heat treated to withstand higher tightening torque
  • Split seam can be pressed-into assembly
  • Suitable for molding-in with viscous materials
  • Available in oval shape for extra clearance on one axis.
Your Total Assembly Solution

Installation Technology for Compression Limiters

SPIROL offers installation equipment designed specifically for cost-effective and high quality installation of Compression Limiters into your molded plastic assembly. Our Compression Limiter Installation Equipment range from manual to fully automatic machines with statistical process control and error-proofing options. We are the only company of our kind that offers the total integrated solution.

Explore Compression Limiter Installation Equipment

Application Success Stories

Local Design, Global Supply.

SPIROL has Application Engineers throughout the world to assist you in your designs, supported by state-of-the-art manufacturing centers and worldwide stocking facilities to simplify the logistics of delivering your product.

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