What Is a DOT Fitting?
"DOT" refers to the U.S. Department of Transportation. A DOT fitting is a tube or hose end fitting for the air brake system of a truck, trailer or bus, made to meet the Department's safety standard FMVSS 571.106. The term covers push to connect fittings, which seal by inserting the tube, and compression fittings, which seal with a nut and sleeve. Air brake lines carry the compressed air that applies the brakes, so air leakage or tube separation can compromise braking performance; that is why DOT fittings are regulated rather than treated as general pneumatic parts.
What FMVSS 571.106 Covers
FMVSS 571.106 is the U.S. Federal Motor Vehicle Safety Standard for brake hoses, brake tubing and their end fittings. It sets the performance that air brake hose, tubing and fittings must deliver before use on vehicles sold in the United States, in areas such as pressure, pull strength and resistance to temperature and vibration. The standard also requires manufacturers to mark compliant tubing and fittings with "DOT", so the marking is the manufacturer's own certification of compliance. Guang Yang DOT fittings, in both inch and metric sizes, are manufactured to meet FMVSS 571.106 for air brake applications.
Where DOT Fittings Are Used
DOT push to connect air fittings connect the air lines in compressed air brake systems on heavy vehicles, where the brake system has to hold pressure under constant vibration. Guang Yang DOT fittings are used on trucks, trailers and buses, and on custom-built vehicles that run air brake or air-assisted systems.
How DOT Push to Connect Air Fittings Work
A push to connect fitting typically has three working parts: a grip ring that bites into the outside of the tube, an O-ring that seals against it, and an inner tube support that keeps nylon tubing from collapsing under the grip. To install, cut the tube square and push it into the fitting until it bottoms; the grip ring holds it and the O-ring seals. To remove, depressurize the system first, then press the release collar and pull the tube out. The tube connection does not require tightening a compression nut, which is why push to connect DOT fittings are faster to install and service in the confined spaces of a chassis; threaded ports are still installed to the specified procedure.
Guang Yang DOT fittings are made of brass for strength and corrosion resistance, and are designed to be released and reused.
Push to Connect vs. Compression DOT Fittings
Both types are used in DOT air brake systems, and the choice depends on the tubing, the fitting specification and the installation conditions. Push to connect fittings seal by inserting the tube, which makes installation faster and removal simpler. Compression fittings seal with a nut and sleeve tightened onto the tube; Guang Yang's nut-and-sleeve fittings for nylon air brake tubing are listed under NTA Fittings.
FAQs
DOT fittings are tube fittings for the air brake systems of commercial vehicles, built to meet the U.S. Department of Transportation standard FMVSS 571.106. The term covers both push to connect and compression types.
Push to connect fittings seal by pushing the tube into the fitting, with no nut or tool. Compression fittings seal with a nut and sleeve that are tightened onto the tube. Both are used in DOT air brake systems; push to connect is faster to install and service in tight spaces.
Inch sizes from 5/32" to 3/4" tube OD with NPT threads from 1/16" to 3/4". Metric tube OD and M thread versions are listed as separate models.
Yes. Metric tube sizes are identified by a tube OD given in millimetres. Thread type is a separate specification: an M-thread fitting may be made for inch or metric tubing, so check both the tube OD and the thread on the selected part number.
Yes, provided the fitting and the tube end are undamaged and the manufacturer's reuse guidance is followed. The tube can be released and reconnected without replacing the fitting.
In Taiwan, at the Guang Yang Industrial Works plant.
Nylon air brake tubing is light, flexible and resistant to vibration and road chemicals, and can be routed through a chassis without bending tools. Push to connect fittings suit it because they grip and seal the tube in one push, with the inner support keeping the tube from collapsing.
No approval is issued. NHTSA does not approve individual fittings; the manufacturer certifies that the fitting meets the applicable requirements of FMVSS No. 106 and marks it "DOT" to show that certification.
In designs that use one, the inner support holds the tube wall against the O-ring and grip ring. Nylon tubing is softer than metal, and without support the grip ring could deform the wall and the seal could leak under pressure or vibration.
Working with Guang Yang on DOT Fittings
Guang Yang develops and manufactures brass DOT fittings in Taiwan, in inch and metric sizes for air brake systems on trucks, trailers and buses. To discuss sizes, configurations or quantities, send the tube OD, thread size, configuration and quantity to ky@guangyang-ky.com or use the contact form.
