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Helical Products Company, Inc.

Frequently Asked Questions

Are custom couplings more expensive than the standard couplings?

No, the engineering process required to create your custom HELI-CAL® Flexure is completely free and is part of our committed service to you. Pricing is a function of the complexity of the design and the material specified.

Are the parts listed on the website the only ones Helical manufactures?

No, the couplings listed in the series charts are just the most common products. We do have relieved and non-relieved couplings as well as the ability to mix metric and inch bore sizes.

Do special or non-standard couplings take longer to manufacture?

No, just because they are referred to as “non-standard” does not mean that we may not already have these products in our inventory.

Do you have a solid model of your catalog couplings?

Yes, solid models are available via a link on each specific series page.

Do you have somebody in my area that can enlighten me on your product face-to-face?

Yes, we have both domestic and international sales reps that are very knowledgeable and factory trained on our products. Simply click on the Sales Rep link and select your region to find out who can help you.

Do you only manufacture couplings, machined springs and u-joints?

No. We don’t like to limit the HELI-CAL Flexure to those 3 categories. The HELI-CAL Flexure can be used anywhere where flexibility or motion control are needed. Have a new challenge for us? Do not hesitate to call our engineers today!

Does your company manufacture thread inserts?

No, that company is Helicoil. They can be reached at

Explain the terms “single start” and “multiple starts”.

A single start spring is a single continuous coil element which starts at one end and terminates at the other end. This configuration is common to most springs. A “double start” spring has two intertwined continuous coil elements phased 180 degrees apart. In effect, this puts two independent helixes in the same cylindrical plane. Multiple start flexures such as triple start etc. are similar extensions of the concept.

I can’t find this part number online, is it a good part number?

Just because you don’t see a part number listed on our website doesn’t mean that it isn’t an allowable part. Not all combinations of bores are listed online. We also manufacture many special designs that are not listed online. Please contact us to verify if your part number is correct.

What are machined springs?

A Helical machined spring is a single piece of material machined into a spring configuration and offering the traditional load cases of Compression/Extension, Torsion, Lateral Bending and Lateral Offset. Key to the versatility of the machined spring is the HELI-CAL Flexure, a flexible helix beam concept. Because Helical springs are “machined” to specific design requirements, they provide more precise performance, attachment features and functions than more traditional types of springs.

What are some of the benefits of multiple start flexures?

Multiple start flexures are beneficial because they not only provide redundant elastic elements should a failure occur, but a failed element (coil) will be physically trapped by the remaining ones.

A multiple start compression or extension spring is balanced when a load is applied, which prevents tipping. Traditional wire springs and single start machined springs have an un-resolved moment when a load is applied. A coupling with a multiple start flexure will have a stiffer torsional rate and can transmit more torque compared to a single start flexure.

What does “relief” mean for a coupling?

A coupling with relief allows both shafts to enter the flexible region. The diameter through the flexible part of the coupling is larger than the diameter of the two shafts. The ends of the two shafts can operate very close together when a relieved coupling is used. For a non-relieved coupling each shaft must not go into the flexible region. In some cases there will be a step to prevent the shaft from entering the flexible region.

Why choose machined springs over traditional wire-wound springs?

With machined springs, desired features or functions can be machined integral to the spring, therefore eliminating complex or expensive wire-wound spring assemblies. Features and functions can include: custom attachments, precise spring rates, multiple start coils, and other special characteristics. These aspects are generally not possible with traditional springs. There are big differences in performance, reliability, versatility, integrity, and cost effectiveness. For more information, explore our white paper.

Still have questions? Feel free to call us at (877) 353-9873 or shoot an email to

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