In a 3/4" rigid to EMT (Electrical Metallic Tubing) coupling, various types of seals can be used to ensure leak-tight connections between the rigid conduit and the EMT. The choice of seal depends on factors such as the application requirements, environmental conditions, and installation preferences.

Here are some common types of seals used in 3/4" rigid to EMT couplings:

1. Compression Seal: A compression seal is a rubber or elastomeric gasket that is compressed between the rigid conduit and the EMT when the coupling is tightened. This seal forms a tight and reliable connection, 3/4 rigid to emt coupling  preventing moisture, dust, or contaminants from entering the conduit system.

2. Threaded Seal: Threaded seals use threads on the coupling and the conduit to create a tight seal when screwed together. The threads form a mechanical barrier that prevents the ingress of liquids or debris into the conduit, ensuring a leak-tight connection.

3. O-Ring Seal: An O-ring seal is a circular elastomeric ring placed inside the coupling to provide a sealing interface between the rigid conduit and the EMT. When the coupling is tightened, the O-ring compresses against the surfaces of the conduit, creating a watertight seal.

4. Tapered Thread Sealant: Tapered thread sealant, such as Teflon tape or pipe dope, can be applied to the threads of the coupling before installation. This sealant fills in any gaps or irregularities between the threads, providing an additional layer of protection against leaks.

5. Liquid Sealant: Liquid sealants, such as pipe thread sealant or pipe joint compound, can be applied to the threads or mating surfaces of the coupling and conduit before assembly. These sealants harden over time, forming a durable and resilient seal that withstands environmental factors and pressure changes.

6. Compression Ring Seal: Some couplings feature a compression ring or ferrule that compresses against the conduit's surface when tightened, creating a secure seal. This type of seal is particularly effective in high-pressure or vibration-prone environments.

7. Rubber Bushing Seal: A rubber bushing or grommet can be inserted into the coupling to provide a flexible and resilient seal between the rigid conduit and the EMT. The rubber material conforms to the contours of the conduit, ensuring a tight and secure fit.

It's essential to select the appropriate seal type based on the specific requirements of the application and ensure proper installation techniques to achieve a leak-tight connection between the 3/4" rigid conduit and EMT. Additionally, adherence to relevant codes and standards governing conduit installations is necessary to maintain system integrity and safety.