FIELD LOK 350® Gaskets

The gold standard for push-on joint restraint. U.S. Pipe's FIELD LOK 350® Gasket is an extremely successful, trouble-free means of joint restraint in 4" - 24" sizes for well over one million Ductile Iron pipe and fitting joint assemblies across North America.

  • No pipe surface preparation or grooving is required for field cut pipe other than the cut end needing to be beveled as required for any push-on joint spigot end.
  • Joints are restrained without thrust blocks, bolts, grooves, rods, clamps or retainer glands, resulting in savings of labor, material and time.
  • Available in 4" - 24" sizes (350 psi)
  • For sizes larger than 24" see TR Flex® or HP LOK® Restrained Joint products.

Product Downloads


  • FIELD LOK 350® Gaskets

    View and/or download to learn more about U.S. Pipe's FIELD LOK 350® Gaskets.

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  • FIELD LOK 350® Alternative Notice

    Please read this important notice regarding alternative restrained joint gaskets and ensure you ask for the ORIGINAL FIELD LOK 350® when you need restraint!

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Product Information


FIELD LOK 350® Gaskets Product Animation
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FAQs // FIELD LOK 350® Gaskets

U.S. Pipe does not recommend the use of FIELD LOK® Gaskets with a TYTON® Plugs. Due to the fact that you cannot get the gasket out unless you cut the pipe bell off because of the flange on the end of the plug. If the plug is pushed in too deep then the set screw holes can be in the gasket bulb causing it to leak. Since the installation was performed with a FIELD LOK Gasket, you cannot pull it out and the fitting or pipe bell would have to be scrapped.

While other manufacturers are licensed to manufacture the TYTON JOINT® through 24" diameter, only TYTON JOINTS® conforming to current joint configurations which allow 5 degree joint deflection are applicable with FIELD LOK 350® gaskets.

FIELD LOK 350® gaskets cannot be used for bridge crossings. The FIELD LOK 350® gasket is a friction restrained joint and due to the fact that bridges are subject to vibration from vehicles traveling over the bridge, there is a possibility that the gasket could work itself lose. U.S. Pipe's recommendation for bridge crossings is TR FLEX® pipe.

To install the gasket correctly in the groove in the bell, it must be uniformly distributed around the interior of the bell circumference. To do this, the gasket must be looped as it is initially placed in the bell. As a general rule:

4" through 12" gaskets generally require one loop. In cooler weather it may be easier to install the 10" and 12" gaskets using two loops placed at the twelve and six o'clock positions.

14" through 20" gaskets generally require two loops but three may be necessary, placed at the twelve and six o'clock positions.

24" through 36" gaskets generally require four loops, spaced approximately 90° apart. Put the bottom loop in first to prevent debris from being introduced into the joint.

42" and 48" gaskets generally require six loops, spaced equally around the circumference of the bell. Put the bottom loop in first to prevent debris from being introduced into the joint.

54" through 64" gaskets generally require eight loops, spaced equally around the circumference of the bell. Put the bottom loop in first to prevent debris from being introduced into the joint.

In cooler weather, it is usually a good idea to warm the gaskets before trying to install them or store them in a warm environment.

Never lubricate the gasket or gasket groove prior to installation of gasket into the bell.

The FIELD LOK 350® gasket and TR FLEX® joint are both boltless restraints. This saves time by not having to tighten any nuts & bolts as well as preventing possible leaks where a bolt wasn't tightened.

U.S. Pipe's primary method of thrust restraint are restrained joints.

A column of liquid moving through a pipeline has momentum or force that tends to separate the joints at changes in direction (bends and tees), stops (plugs, caps, or closed valves), and changes in size (reducers). Some means must be used to prevent joint separation to maintain the integrity of the pipeline. Three such means are thrust blocks, tie rods, and restrained joints.

Thrust blocks are usually poured-in-place concrete.  They must be engineered with full knowledge of the pipeline operating characteristics and of soil type and bearing strength. They must bear against virgin soil, because thrust forces in the pipeline are transmitted through the thrust block to the soil.  Depending on these conditions, thrust blocks can be quite massive. The use of thrust blocks can delay completion of the project to allow the concrete to cure adequately before applying test pressure to the pipeline. If future construction disturbs the thrust block or the surrounding soil, joint restraint and the integrity of the pipeline can be jeopardized.

Tie rods usually involve some sort of fabricated steel harness on either side of the joint held together by tie-rods. This type of joint restraint is generally labor intensive. A tie-rod type of joint restraint must be adequately protected against weakening by corrosion, or else the joint restraint and integrity of the pipeline can be jeopardized.

Restrained joints are designed to hold the joint together against a rated pressure while the pipeline transfers the thrust force to the surrounding soil envelope. In order to calculate the footage of restrained pipeline necessary for the thrust force to be fully dissipated to the soil, it is necessary to know pipe diameter, maximum anticipated internal pressure, depth of cover, soil type, and trench construction type, as well as the configuration (e.g., bend angle) requiring restraint. The calculated restrained footage must be installed on each side of the fitting. Since polyethylene encasement for external corrosion protection reduces the friction between the pipeline and the surrounding soil, the calculated restrained footage is usually multiplied by a factor of 1.5 for pipelines where polyethylene encasement is to be installed.

Mechanical joint retainer glands, both common and proprietary design, are available for use where such devices must be used (e.g., a special valve or meter). However, U.S. Pipe does not recommend their use. Restrained push-on joints manufactured by U.S. Pipe are less susceptible to external corrosion, offer appreciably more deflection, and are much less labor-intensive to install.

Download our listing spreadsheet to learn more:

UL and FM Listings

Deflection of the pipe should occur after the plain end has compressed the gasket but prior to the plain end being homed into the bell. See FIELD LOK 350® animation for complete details of assembly.

AWWA/ANSI C110/A21.10: Ductile Iron and Gray Iron Fittings, 3 in. through 48 in. For Water and Other Liquids

AWWA/ANSI C153/A21.53: Ductile Iron Compact Fittings, 3 in. through 24 in. and 54 in. through 64 in. for Water Service

AWWA/ANSI C111/A21.11: Rubber-Gasket Joints for Ductile-Iron Pressure Pipe and Fittings

AWWA/ANSI C104/A21.4: Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water

AWWA/ANSI C116/A21.16: Protective Fusion Bonded Epoxy Coatings for the Interior and Exterior Surfaces of Ductile-Iron and Gray-Iron Fittings for Water Supply Service

AWWA/ANSI C105/A21.5: Polyethylene Encasement for Ductile-Iron Pipe Systems

AWWA/ANSI C600: Installation of Ductile-Iron Water Mains and their Appurtenances

Pulling back on the FIELD LOK 350® gasket causes the stainless steel locking segments to engage the pipe, activating the restraint mechanism. Pulling back on the TR FLEX® pipe puts the joint in tension as well as taking up the "slop" in the joint. If this is not done, the line will "grow" when pressure is introduced to it which could cause problems.