3/4″ Manual Reset Snap Disc Thermostats

Senasys manufactures 3/4″ Manual Reset Snap Disc Thermostats, 404 series. Our manual reset thermostat switches are ideal when you want to call special attention to a temperature malfunction. Because the switch needs to be manually reset, a human must interact with the switch and solve the problem before the equipment or appliance can work again.


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


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


All of our snap disc units are UL approved (USR).


Designed & manufactured in Eau Claire, WI, U.S.A.

The 404 series is our 3/4″ manual reset snap disc. This series is ideally suited for applications where you want to call special attention to a specific temperature malfunction. The 404 series feature a trip-free operation. Physical depression of the reset button holds the contact open and renders the device inoperative until the reset button is released.

Our 404 manual reset snap disc thermostats have a temperature range of 100-350°F, ±25°F. Many standard temperature options are available, or we can easily design a customer temperature range to suit your application requirement.

Product Specifications

  • 3/4″ Bi-Metal Snap Action Disc
  • Manual Reset
  • Breaks on temperature rise
  • SPST (Single Pole, Single Throw)
  • 25 Amps @ 120VAC, 6,000+ cycles
  • Temperature Range of 100°-350°F, ±25°F differential
  • Available with exposed caps to provide a faster response time.
  • Special black discs can be used to further improve the response to radiative heating in exposed units.
  • Available with a variety of mounting brackets
  • Variety of terminal options available.
  • UL Listed
  • 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. Additionally, this has allowed us to expand our catalog offering to meet other application requirements, including:

  • Ratings up to 45A@250VAC
  • 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 below.

Standard Direct Mount
Electric Heat Direct Mount
Notched Bracket Surface Mount
Large Surface Mount
Small Flange Surface Mount
Airstream Mount

Terminal Options

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.

1/4″ Quick Connect Terminals
Screw Terminals
Electric Heat Terminals

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


Open 120°F ±5°F


Open 150°F ±5°F


Open 190°F ±5°F


Open 200°F ±7°F


Open 225°F ±7°F


Open 250°F ±8°F


Open 300°F ±8°F


Open 350° ±8°F

Common Applications

Our 3/4″ manual reset snap disc thermostats are found in a variety of applications. Choose a category below to learn more.

Thermostat Switches in Food Equipment
Food Equipment
Snap Disc Thermostat Controls Generator
Other Custom

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.

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.

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.

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 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.

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.


404 Series


60T Series


SE/SES Series

3/4″ Bi-Metal Disc

Enclosed or Exposed

Manual Reset
Fixed Temperature 100°F to 350°F

Open on Temp Rise

Single Pole, Single Throw


25 Amps @ 120VAC

+6,000 cycles

Variety of Mounting Options
Variety of Terminal Options
UL Listed
Made in U.S.A.

Build A Thermostat

Follow the below nomenclature guide to determine the 3/4″ manual reset thermostat to meet your application requirements.

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

404 Snap Disc Thermostat Nomenclature

Request A Quote

Complete the form below with your application information, and a product specialist with follow up with you in 1-2 business days.

    Your Name (required)

    Your Company

    Your Email (required)

    Telephone Number (required)


    Your Message