STEMCO, a division of senasys

1/2″ Epoxy Sealed Snap Disc Thermostats

Senasys’ 1/2″ epoxy sealed snap disc thermostats are designed for extended use in extreme environments , built using our patented metal sleeve rivet construction and sealed to protect against salt spray, water, moisture and heat .

custom options

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

high quality

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


Senasys products are UL/cUL Recognized.

made in u.s.a.

Senasys products are designed & manufactured in Eau Claire, Wisconsin, U.S.A.

The 431 series 1/2″ epoxy sealed snap disc thermostats are used whenever a moisture or dustproof enclosure is required for safe, sensitive and reliable operation. A polypropylene boot enclosure filled with epoxy resin covers the thermostat. The bi-metal disc control element is in close proximity to the sensor cap to provide rapid response to temperature changes.

Since the bi-metal disc used in the Type 431 thermostat is thermally and electrically insulated the bi-metal disc reacts only to the temperature of the controlled device or medium surrounding the disc. Instantaneous, positive action of the disc prolongs thermostat life by minimizing arcing and eliminates chattering, false cycling and electrical interference with radio and television reception. Long life is assured with wiping contacts.

The temperature range determines when the thermal switch will close, or engage the electrical circuit, and when it will automatically reset, or open. A specific temperature range may be designed according to your application needs, or choose from our standard ranges.


  • 1/2″ Bi-Metal Snap Action Disc
  • High environmental exposure temperature range of -40°F to 200°F (-25°-105°C).
  • Differential temperature range of 15-80°F (-9 – 25°C).
  • Automatic Reset
  • Single-pole, single-throw (SPST)
  • Rated up to 15 Amps @ 120VAC, 100,000 cycles
  • Variety of mounting options available such as pipe & stud mounts.
  • Variety of wire lead options available, standard: 18AWG – 12″ or 72″, covered with 1/32″ or 1/16″ thick 100°C plastic insulation. Other custom wire leads, such as gauge, color, length, & connectors available. Contact us for more information.
  • UL Approved
  • Made in U.S.A.

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.

Mounting Options

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

Direct Mount
Surface Mount
Pipe Mount
Threaded Stud Mount
NPT Threaded Mount
Large Surface Mount

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 431 series 1/2″ epoxy sealed 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

Frequently Asked Questions


What is the DC voltage rating on the 431 series?

Our epoxy sealed thermostat switches are UL rated for 100,000 cycles 15 Amps at 120VAC / 10 Amps at 240VAC, and 0.5 Amps at 24VDC. We did some additional testing in house. Check out our results here!

Do these switches meet the UL94 flammability standards?

Our complete switches aren’t rated for UL94, or any other particular flammability rating for that matter, individual components are. We did some testing in-house as well. Check out the results here!

What custom temperatures are available?

For small quantities, we can build anything from 0°F to 220°F. Contact us for higher temperatures.

How much power does a snap disc thermostat use?

A snap disc does not use any power. Instead it acts as a circuit breaker for a system.

What material are snap discs made from?

The body of the switch is plastic, and the mounting cap is either steel, aluminum, or brass.

Where are Senasys snap disc thermostats manufactured?

Our products are designed and manufactured in Eau Claire, WI, U.S.A., and sold globally! We also have relationships with suppliers overseas to provide a more low cost solution when required.

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 are the options for the wire leads?

Our standard wire leads are black, 18 AWG at 12″ or 72″ length. We recommend the 72″ length, and then cutting down to what you need. We have other options available including color, lengths and gauge sizes. Click here to learn more.

What is the durability of the epoxy sealed thermostats under water?

Senasys manufacturers two different lines of sealed thermal switches,  431 series and 2570 series, which are  UL873 approved to be hermetically sealed. Our sealed snap disc thermal switches are commonly found in environments where condensation, dust or other material may be present.

Senasys performed a series of tests with our sealed thermostat switches by submerging them into fresh water and salt water. Click here to see the results!

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.


431 Series

Thermodisc (TOD)

39T Series




T16 & T17 Series

1/2″ Bi-Metal Disc
Automatic Reset
Temperature Range -40°F to 200°F
15 Amps at 120 VAC

+100,000 cycles

Single Pole, Single Throw


Surface, Airstream, Pipe & Stud Mounting Options
Custom Wire & Termination Options
UL Listed
Made in U.S.A.

Build Your Thermostat

Follow the below nomenclature guide to determine the 431 series automatic reset thermostat to meet your application requirements.

Request A Quote

For technical support, price & availability, complete the form below. Our team of product specialists will follow up with you in 1-2 business days.

    Your Name (required)

    Your Company

    Your Email (required)

    Telephone Number (required)


    Your Message