Get unique, complex parts easily. No matter your requirements, Master Spring creates hard-to-produce coil springs and wire forms.

Custom Wire Forms

Let us help you create the custom wire form you need, from S-hooks and J-hooks to utility hooks and more.


We work closely with customers across a wide range of industries, helping them design and manufacture made-to-order parts.

Master Spring Advantage

Why choose Master Spring? We prioritize customer-focused collaboration, modern equipment and the latest technology to make your parts per print.

Custom, Made-to-Order Extension Springs

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Unique Tension Springs for Many Applications

Master Spring custom manufactures complex, custom extension springs from round wire, including extension springs that secure the doorframe to housings for commercial lighting fixtures, extension springs for heating elements used on beverage ice dispenser agitator motors, and extension springs for bill weights in point-of-sale (POS) cash drawers.

Stainless steel extension spring

Drain Pan Extension Spring

Part Names: Stainless steel extension spring, extended hook extension spring

Industry: Hardware and fasteners: Employee safety equipment

Application: Used in an eye/face wash and shower safety station; spring keeps recessed drain pan closed in a vertical position

Material: : 0.067” type 302 stainless steel wire

Special Features: : Springs are passivated; center rectangular hook with 11/64” gap on one side; other end has a center extended hook with eyelet that is in-line with other side

Laundry basket extension spring

Basket Truck Lift Spring

Part Names: Laundry basket extension spring, large extension spring, side-loop extension spring

Industry: Hardware and fasteners: Laundry and housekeeping basket trucks

Application: Extension springs lift bottom of laundry basket truck as load gets lighter

Material: 0.120” galvanized hard-drawn MB spring wire

Special Features: 45-degree side loops; each loop is two coils and loops are in-line; oval ring is assembled to one loop

lighting fixture extension springs

Retractable Cable Extension Spring

Part Names: Stainless steel extension spring, lighting fixture extension spring, retractable cable extension spring

Industry: Commercial LED lighting for challenging environments

Application: Retractable cable and extension spring secures doorframe to lighting fixture housing

Material: 0.033” stainless steel 302 wire

Special Features: Open and centered loops in-line

Door Micro Extension Spring

Door Micro Extension Spring

Part Names: Small stainless steel extension spring, semiconductor wafer case spring, extended hook extension spring

Industry: Semiconductor device fabrication industry

Application: Spring used on door of case that transports, stores and protects semiconductor wafers and photomasks

Material: 0.013” type 302 stainless steel wire

Special Features: Long extended hooks

3 Center hook extension springs

Pressure Roller Extension Spring

Part Names: Center hook extension spring, currency scanner extension spring

Industry: Currency scanners and sorters

Application: Extension spring provides feed roll pressure to notes in currency scanners and sorters

Material: 0.037” phosphate-coated music wire

Special Features: Center hooks in line; gap is 0.090” to 0.130”; finish is zinc trivalent with bake

Stainless steel extension spring

Agitator Motor Heater Spring

Part Names: Stainless steel extension spring, heating element extension spring, German loop extension spring

Industry: Beverage dispensing and cooling equipment

Application: Extension spring works as a heating element to keep ice agitator motor warm in beverage dispensing equipment

Material: 0.025” type 302 stainless steel wire

Special Features: German closed loops in-line

Active-coil Helical Extension Spring

Part Names: Trampoline spring, physical therapy rebounder spring, extension spring

Industry: Hardware and fasteners: Physical therapy products

Application: Extension springs return the trampoline mat to starting position in plyometric rebounder

Material: 0.138” phosphate-coated music wire

Special Features: Center hooks in line; gap is 3/8” to 7/16”; finish is zinc trivalent with bake

Snowplow extension spring

Extension Spring, .375” OD x 2.5” Long

Part Names: Snowplow extension spring, center-loop extension spring, stainless steel extension spring

Industry: Hardware and fasteners: Professional snowplow and ice removal equipment

Applicatoin: Provides tension on a coupler stop pin on snowplow equipment

Material: 0.049” type 302 stainless steel wire

Special Features: Center loops in line +/- 30 degrees; fully closed loops

Cash drawer extension spring

Currency Hold-down Extension Spring

Part Names: Cash drawer extension spring, cash register extension spring, side-loop extension spring

Industry: Hardware and fasteners: Point-of-sale (POS) heavy-duty cash drawer

Application: Extension springs provide tension on currency hold downs in heavy-duty till

Material: 0.020” galvanized music wire

Special Features: Full side loops in-line

Stainless steel clutch spring

Clutch Garter Spring

Part Names: Stainless steel clutch spring, fun-kart clutch spring, small index extension spring

Industry: Hardware and fasteners: Fun-kart and four-cycle racing karts

Application: Extension spring works as a garter spring in an automatic centrifugal clutch on a fun kart

Material: 0.057” type 302 stainless steel wire

Special Features: Extremely small spring index (ratio of mean coil diameter to wire diameter); machine loops (same as German hooks or twist loops); one loop is closed; second loop has a gap

Hold-down Relay Spring

Hold-down Relay Spring

Part Names: Extended-hook extension spring, stainless steel extension spring, relay hold-down extension spring

Industry: Industrial electrical control and monitoring products

Application: Hold-down spring to hold relay onto panel mounted socket

Material: 0.026” type 302 stainless steel wire

Special Features: Extended side hooks with two closed loops perpendicular to the leg on each end

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Custom Extension Spring Capabilities

As an industry-leading extension spring manufacturer, we are your one-stop source for precision, custom extension springs with a wide range of hook and loop options and wire sizes. Learn about our extensive extension spring production services—from custom hooks and loops to rapid prototyping, special packaging, assembly services and more.


Master Spring has the CNC machinery and tool making capability to automate the manufacturing of custom extension springs (also called tension springs or expansion springs) with your unique loops:

  • Extended hooks, German loops, crossover loops, machine loops, twist loops and side loops
  • Hook shapes that are traditional, rectangular, complex or that have eyelets
  • Side or centered loops that are angled 90 degrees or 45 degrees from the spring body
  • Closed or open loops with a specified gap dimension
  • Single loops or double loops
  • Loops in line with each other or at certain degrees relative to each other
  • Swivel hooks, flat stock hooks or oval rings assembled to extension spring /extension-spring-hooks.jpg N/A Eight types of tension spring hooks

Tension Spring Hooks

Five types of expansion spring loops

Expansion Spring Loops


Need help creating a new design or solving a problem with your existing extension spring? Looking for help engineering a German loop extension spring? Our engineers use a spring design software to review your extension spring for functionality and manufacturability and to look for improvements and cost savings. We check if the tension spring has too much stress in its deflection range and if the spring’s extension design meets your required tolerances. In addition, we determine if the estimated life cycle is greater than you need and if there are any other design warnings.

With over 75 years of custom extension spring manufacturing experience, we solve the toughest challenges. Contact us if you need samples quickly or to setup a discussion with a knowledgeable engineer to review and advise on your design.

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Master Spring tailors extension spring packaging to meet your unique assembly line and finished product needs. Our custom packaging solutions include tangle-free packing for efficient assembly operations, a pre-determined standard quantity per bag and individually bagged and labelled parts ready to ship to your customers.

Contact us today for more information about our custom extension spring special packaging services.

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Tack board battery connector to prevent coil spring tangling

Tack Board Battery Connector

A small bag of custom coil springs with black finish

Small Bag of Custom Coil Springs

Helical springs strung on wire loops to prevent tangling

Helical Springs Strung on Wire Loop

Custom wire forms zip tied in bundles

Zip Tied Wire Forms

Wire clips nested in two labelled cardboard boxes

Nestled Wire Form Clips

Multiple springs layer-packed to minimize tangling

Multiple Springs Layer-packed

An individually bagged and labelled custom spring clip

Individually Bagged Spring Clips


Let Master Spring’s extension spring assembly services lower your production costs by reducing the components you need to purchase and inventory. We can assemble your tension spring with its mating part and send the sub-assembly to you.

Contact us today to get started with our extension spring assembly services.

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Two wire forms assembled together to create a wire spring latch

Wire Spring Latch

Oval loop assembled to a custom extension spring

Oval Loop Assembled to Extension Spring

Milk Frother

Heat shrink with a black rubber sleeve on a retainer spring

Rubber Sleeve on Retainer Spring

Ball chains assembled to a wire form

Ball Chains Assembled to Wire Form

A trotline clip with a brass swivel hook

Trot Line Clip

Copper clasp assembled to a custom wire form to create a pull pin

Copper Clasp Assembled Pull Pin

Torsion spring assembled to a plastic molded trigger

Torsion Spring Assembled to Molded Trigger


As your trusted extension spring manufacturer, Master Spring’s experience and quality process provide the documentation you require for your extension springs.

We have experience providing a Production Part Approval Process (PPAP) to our customers. After receiving our PPAP report, you can assess our process stability, review our controls to provide conforming product and have an approval outlet for any extension spring design changes.

We create a First Article Inspection Report (FAIR) for each production run. The FAIR indicates the nominal dimensions, tolerances, precise measurements and methods of measurement for a requested quantity. Each FAIR provides a record of the raw material heat number to provide traceability to the batch of wire used for each production run.

Upon request, we can include certificates of compliance, material certificates and finishing certifications with each shipment of extension springs.

Strict vendor management and lot control enable us to comply with regulatory compliances, including Conflict Minerals, DFARS, REACH, RoHS or California Prop 65. Let us know your documentation, certificate and compliance requirements when you request a quote.


Our CNC extension spring machines coil a wide range of wire sizes—giving us the ability to manufacture large extension springs and springs in smaller sizes. With full CNC control of all axes, our machines can manufacture precise, custom extension springs with wire diameters as small as 0.012” or as large as 0.250” (0.30mm to 6.35mm), and any size in between.

As a long-time, reliable extension spring manufacturer, we have invested in a large inventory of extension spring tooling to cover the wire diameter range for each forming machine.


Master Spring maintains strong relationships with local, qualified wire distributors and mills that offer quality wire to meet your specifications. We have years of experience making custom expansion springs from many different material types:

High-carbon Spring Steel Wire : Hard-drawn wire, music wire and oil-tempered

Stainless Steel Wire: 302, 304, 316 and 17-7 PH

Alloy Steel Wire: Chrome silicon

Non-ferrous Alloy Wire: Phosphor bronze, beryllium copper, brass, Monel

High-temperature Alloy: Inconel

Special Purpose Alloy: Elgiloy, MP35N, Hastelloy C276

*Some of the carbon wire types can be pre-plated with a galvanized, zinc-coated finish, a tin-coated finish or Bezinal®-coated finish.

Properties of Materials Guide

Looking for information about common materials used in extension springs? Explore our guide to learn about nominal chemistry, minimum tensile strength, maximum operating temperatures, Rockwell hardness and suitable uses for each material.

Explore the Guide


To complete your custom extension springs, we offer an extensive variety of finishing types. We manage a strong network of local, qualified vendors who offer quality finishes, short lead times and competitive pricing. Learn more about our finishing services below.

Wire forms on a conveyor belt receiving in-line stress relief

In-house Stress Relief

We use in-line ovens at each forming machine to apply low-temperature stress relief. This process alleviates residual stresses produced by prior cold forming and improves the extension spring’s shape memory to maintain its coiled shape.

Five compression springs with shot peen finishing

Shot Peen

Shot peening improves resistance to fatigue, prevents cracking and increases lifecycle. The shot peening process blasts the surface of the wire with steel or glass pellets to create deformations. Our local, qualified vendors specialize in quality shot peening and surface preparation.

Three torsion springs that received tumble deburr treatment


Tumbling improves surface finish by removing unwanted sharp edges and burrs from standard machine cuts.

Six wire forms with black oxide plating


Our large network of qualified platers provides a wide range of plating finishes such as black oxide, zinc, nickel, tin, trivalent chromate and many more finishes in a variety of colors.

Coil springs and wire forms with powder coat finishing

Powder Coat

Numerous powder coat colors are available for extension springs.

Coil springs with passivate finishing in before and after stages


An acid treatment for stainless steel, passivation removes contaminants and improves corrosion resistance. We recommend passivating stainless steel extension springs used in the medical and food industries.

Custom springs with electropolish finishing in before and after stages


Electropolish brightens, removes burrs and passivates. For best results, use it on 300-series stainless steel types.

Coil spring types with in-house dye and paint finishes

In-house Dye or Paint

Color coding helps identify and distinguish similar parts in your assembly line. We use an environmentally safe, water-based polymer coating. This coating adheres to the extension spring in-line immediately after oven stress relief.

Two custom coil springs with e-coat finishing in black


E-coat is an electrically applied paint coating that is used as a decorative or protective finish. It enhances appearance while also protecting the surface of extension springs.

Custom wire forms with Magni 525 coat finishing in before and after stages

Magni Coat

Magni coat is a thin, paintable coat that provides exceptional corrosion protection in extreme environments. It is superior to zinc-plating.

Two wire forms with black plastic coating, called plastisol

Plastic Coat

We can add a plastic coating to your extension springs in a variety of available colors.

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Custom Extension Spring Design for the Gaming Industry

See how Master Spring’s engineering expertise and finishing capabilities increased the life cycle of a drop-target extension spring and made assembly easier and error free.

Master Spring Advantage

With expert engineering assistance, forming machines that manufacture a wide variety of custom hooks and loops, in-line monitoring and the latest design software tools, we make it possible to manufacture complex extension springs.

Learn More About Us


  • Engineering assistance to overcome extension spring design obstacles and offer you a solution
  • Skilled machine setup technicians who can meet your unique tension spring dimensions
  • In-house, experienced tool makers who design and manufacture custom tools to form your unique hooks and loops
  • Custom-tailored packaging, assembly and finishing services


  • All-servo, high-speed CNC forming machines that can create custom extended hooks, German loops, crossover loops, machine loops, twist loops and side loops  with specified gap dimensions and relative loop positions
  • Laser sensors and touch probes to automatically monitor extension spring dimensions in-line
  • CNC milling machines to custom manufacture extension spring looping tools
  • Spring testers to measure extension spring initial tension, loads and rates


  • JobBOSS ERP software to integrate quoting, job routing, purchase orders, shipping and invoicing
  • Spring Manufacturers Institute’s Advanced Spring Design Software to review your extension spring’s design and recommend improvements
  • SOLIDWORKS CAD software for a collaborative design process
  • MasterCAM software to design and manufacture tools for making custom hooks and loops
  • Dozuki video software to document and standardize work instructions for repeat setups
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Contact Master Spring

Need a custom wire form or coil spring? We make it work. Fill out the contact form and a representative will respond within 1 business day. If you have a PDF or CAD file, you can submit to request a quote.


Request a Quote



Your Team For Innovative Wire Forming

We provide solutions for complex, high-quality
wire forms and coil springs.

78 Congress Circle West, Roselle, IL 60172

P: 708.453.2570 | Contact Us

We do not stock standard springs,
we make made-to-order custom springs.