STEMCO, a division of senasys

1/2″ Automatic Reset Snap Disc Thermostats

Our 1/2″ automatic reset snap disc thermostats use a bi-metal 1/2″ disc for snap action, positive & instantaneous opening or closing of electric circuits. The 1/2″ auto reset snap disc thermostats have a smaller footprint allowing for a lower cost than our other automatic reset thermostats.

The 1/2″ auto reset thermostat can be specified for heating applications where the contacts break on temperature rise, or for cooling applicants where the contacts break on temperature fall.

We offer two different styles of of 1/2″ auto reset thermostats:

  • Phenolic body (430 series) with a temperature range of 35°F to 350°F.
  • Ceramic body (T24 series) for high temperature applications beyond 350°F.


Designed & manufactured to meet requirements of original equipment manufacturers worldwide.


Senasys products are 100% tested before they leave our facilities.


Senasys products are UL/cUL Recognized.


Snap disc thermostats are designed & manufactured in Eau Claire, WI U.S.A.

Our 1/2″ automatic reset snap disc thermostats have a smaller footprint allowing for a lower cost. The thermostat can be specified for heating applications where the contacts break on temperature rise or for cooling applications where the contacts break on temperature fall. Our thermostats use a bi-metal disc that reacts to temperature changes and ‘snaps’ causing the circuit to open or close.

Since the bimetal disc used in the auto reset thermostat is thermally & electrically insulated from the current carrying parts of the thermostat, the disc reacts to the temperature of the controlled device or medium surrounding the disc. This eliminates chatters, false cycling & electrical interference.

  • 1/2″ Bi-Metal Snap Action Disc
  • Automatic Reset
  • Breaks on Temperature Rise or Fall
  • Single-pole, single-throw (SPST)
  • Rated up to 15 Amps @ 120VAC, 100,000+ cycle life
  • 35°F to 350°F (0°C to 175°C) Temperature Range
  • 15°F to 100°F (-9°C to 37°C) Differential Temperature Range
  • Available with an enclosed or exposed disc, for faster reaction.
  • Multiple mounting options such as pipe mounts & stud mounts
  • Multiple terminal configurations
  • UL/cUL Listed
  • Made in U.S.A.

The temperature range determines when the thermal switch will close, or engage the electrical circuit, and when it will automatically reset, or open. Many temperature ranges are available, or we can easily design a custom temperature range to suit your application.

If you require a hotter temperature of 350°F-450°F , our ceramic style 1/2″ thermostat switches (T24 series) will be best for your application.  Learn more here.

Spacings of at least 1/8″ through air & 1/4″ over surface of insulating material are maintained between bare live parts & normally grounded parts, when installed with insulated mounting bracket. The thermostat without the insulated mounting bracket has a spacing of at least 1/16″ through air & over surface from bare live parts to normally grounded parts. Spacings of 1/32″ through air & 1/16″ over surface of insulating material are maintained between bare live parts of the same polarity of the different switch pole components except at contacts.

For a more economical solution, Senasys has built relationships with overseas suppliers to provide our customers thermostats at a lower cost, with the same high quality as our snap disc thermostats built in the U.S.A. Additionally, this has allowed us to expand our catalog offering to meet other application requirements, including:

  • Ratings up to 25A@277VAC
  • -20°F to 480°F (-30°C to 250°C) Temperature Range
  • TUV Listed

Contact us  for more information.

Mounting Options

With snap discs, different applications will require a different snap disc mounting style. Temperature switches can be installed in a variety of environments, and the right mounting bracket is needed to make sure that the switch is able to perform accurately. Even if a switch functions at the right temperature, the wrong bracket can cause it switch at the wrong time or even not switch at all. See a variety of available mounting options below, or click here to learn more.

If you need a style that isn’t shown here, contact us! We offer custom bracket options as well.

Select from a variety of mounting options, including pipe and stud mounts.

Direct Mount
Surface Mount
Large Surface Mount
Loose Hold Bracket
Airstream Mount
Large Airstream Mount
Threaded Stud Mount
NPT Threaded Mount
Pipe Mount

Terminal Options

Our 430 series is available with a variety of terminal options. Our standard terminals are 1/4″ Quick Connect Terminals.

A variety of terminal bends & orientations are also available. Our standard terminal bends are 0°, 45° or 90°.

Learn more about our terminal options available here.

For other custom options, please  contact us.

Solder Terminals
3/16″ Quick Connect Terminals
1/4″ Quick Connect Terminals
Flat Eyelet
Long Strap
Offset Eyelet
Barrel Solder
Wire Crimp
Reinforced Ribbed Retainer

Standard Temperature Options

Below is a list of our common, off the shelf, bi-metal temperature options. Custom temperature options available. Please contact us.

Disc Number


Close 45°F ±5°F Open 34°F ±5°F


Close: 60°F ±5° Open: 50°F ±5°


Close 85°F ± 5°F Open 70°F ± 6°F


Close: 100°F ±5°F Open: 85°F ±5°F


Close 125°F ± 7°F Open 105°F ± 7°F


Close: 150°F ±5°F Open: 135°F ±5°F


Close: 175°F ±5°F Open: 160°F ±5°F


Close: 180°F ±5°F Open: 160°F ±5°F


Close: 190°F ±5°F Open: 175°F ±5°F 


Close: 200°F ±5°F Open: 185°F ±5°F


Close: 220°F ±5°F Open: 200°F ±5°F


Close: 250°F ±5°F Open: 230°F ±5°F

Disc Number


Open 45°F ± 5°F Close 34°F ± 6°F


Open: 60°F ±5°F Close: 45°F ±5°F


Open: 75°F ±5°F Close: 60°F ±7°F


Open 100°F ± 5°F Close 85°F ± 5°F


Open 125°F ± 5°F Close 105°F ±5°F


Open: 150°F ±5°F Close: 135°F ±5°F


Open: 170°F ±7°F Close: 155°F ±7°F


Open 180°F ± 5°F Close 155°F ± 5°F


Open 190°F ± 5°F Close 170°F ± 7°F


Open: 200°F ±5°F Close: 185°F ± 7°F


Open: 220°F ±5°F Close: 190°F ±8°F


Open: 250°F ±5°F Close: 230°F ±7°F

Common Applications

Our 1/2″ automatic reset snap disc thermostats are found in a variety of applications. Choose a category below to learn more.

Automatic Reset Thermostat Switch Controls Food Equipment
Food Equipment
Limit Switch for Coffee Maker
Home Appliances

Frequently Asked Questions


What is a bi-metal snap disc?

Our snap disc thermostats are created with bimetal discs in them that react to temperature changes (rise or fall) and ‘snap’ causing the circuit to open or close. We form our discs from one of three bimetal compositions. Click here to learn more.

How are snap disc thermostats tested?

Senasys tests our snap disc thermostats through air, fluid, hot plate and other testing standards. Learn more about our quality inspection here.

What custom temperatures are available?

For small quantities, we can build anything from 0°F to 350°F. Contact us for higher temperatures.

What is the differential of a snap disc thermostat?

For these types of switches 10ºF is about the smallest range they can maintain cost effectively and consistently.

For complex systems actual testing is usually pretty important. We support this process by making it easy to test multiple package styles and disc temps in sequence or all at once just give us a call. Learn more about temperature differentials here.

I have a snap disc thermostat from Thermodisc (TOD), or other manufacturer. Can you provide?

Yes! Senasys can cross reference most Thermodisc and other manufacturers on the market today with our extensive catalog. Send us more details such as drawing, part number and/or description for quote.

I need a custom mounting bracket or terminal. What are your capabilities?

We have the ability to produce most metal component parts in house, and have an extensive supplier catalog that allows us to meet most application requirements. Contact us with your specifications.

When should an exposed snap disc cap be used?

One of the standout characteristics of an exposed cap is its’ use of a black exposed disc. This disc serves as a crucial element in sensing temperature fluctuations swiftly, enabling the switch to respond rapidly to environmental changes. This quick thermal response is especially important in applications where precise temperature control is paramount, such as in thermostats, industrial control systems, and appliances. The exposed caps are available for all non-epoxied snap disc thermostats within the Senasys catalog. 

For more information on exposed snap disc caps, click here

When should gold contacts be used in place of silver?

One of the key advantages of gold contacts is their significantly lower contact resistance when compared to high-current silver contacts. This low resistance translates into improved electrical conductivity, allowing for smoother and more reliable signal transmission. This is especially important in applications where even the slightest interruption or distortion in the signal could lead to critical errors or malfunctions.

For more information on when gold contacts should be used, click here

What is a flange mount?

When it comes to temperature monitoring, precision is key. The standard flange mount plays a vital role in achieving this precision by minimizing the distance between the sensor and the area being measured. This reduced gap ensures that temperature fluctuations are detected and recorded with remarkable accuracy, making it an indispensable tool in industries where temperature control is critical.

For more information on flange mounted snap disc thermostats, click here

My thermostat isn’t operating. What should I test first?

Continuity! Whether you have a hot or cold temperature thermostat, this test is easy and one of the first things we ask customers. Learn how to do so here.

What is the temperature tolerance of my snap disc thermostat?

Our standard tolerance is between 5°F to 10°F, but tighter tolerance options are available. We also offer a min/max type. Click here to learn more, or contact us with your requirements.

Where should I locate my thermostat when installing into my equipment?

The location of the temperature switch inside your heating element should be well thought through. Temperature will change in various locations within the system depending on the heating element location. The further you distance from the heating element, the lower the temperature. Where a temperature switch is located will determine how accurate it can measure and control the system. Senasys typically recommends with all of our temperature switches the closer you can get to the heating element the better for the most accurate reading and fastest response time.

Cross Reference

We are certain of our position at the top so we’re comparing our product with other top products in the marketplace today.

Find further details by visiting this link.


430 Series


36T Series


CA/OA Series

1/2″ Bi-Metal Disc
Automatic Reset

Normally Open, or Normally closed

Fixed Temperature Options 35°F to 450°F
Single Pole, Single Throw


15 Amps @ 120VAC

+100,000 cycles

Surface, Airstream, Pipe & Stud Mount Options
Variety of Terminal Options
UL Listed
Made in U.S.A.

Configure A Thermostat

Follow the below nomenclature guide to determine the 1/2″ automatic reset thermostat to meet your application requirements.

Other custom options such as bracket, pipe mount, terminals and more available. Contact our technical support team with your application requirements for quote.

430 or 432 Snap Disc Thermostat Nomenclature

Request A Quote

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