Compression fittings create a leak-tight mechanical connection to copper, aluminum, brass, and compatible plastic tubing without soldering, brazing, or special tools. A ferrule (sleeve) is compressed against the tubing OD as the nut is tightened, forming a permanent pressure seal rated for water, oil, gas, and most process fluids. Compression fittings are the dominant connection method in HVAC refrigerant lines, residential gas appliance connections, instrument tubing, and light industrial process piping.
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1/8 in. Brass Captive Sleeve Nut -
1/8 in. Brass Compression Union Body -
1/8 in. x 1/16 in. Brass Compression x Male NPT Adapter -
3/16 in. Brass Barstock Compression Elbow -
3/16 in. OD x 1/4 in. Brass Compression x Male NPT Adapter with Sleeve Nut -
3/16 in. OD x 1/4 in. Brass Compression x Male NPT 90-Degree Elbow with Sleeve Nut -
3/16 in. OD x 1/8 in. Brass Compression x Male NPT 90-Degree Elbow with Sleeve Nut -
3/16 in. x 1/8 in. Brass Compression x Male NPT Run Tee -
1/4 in. Brass Captive Sleeve Nut -
1/4 in. Brass Compression Union with Sleeve Nut -
1/4 in. OD x 1/4 in. Brass Compression x Male NPT Adapter with Sleeve Nut -
1/4 in. OD x 1/8 in. Brass Compression x Male NPT 90-Degree Elbow with Sleeve Nut -
1/4 in. White Nylon Compression Union -
1/4 in. x 1/2 in. Brass Compression x Female NPT Elbow -
1/4 in. x 1/2 in. Brass Compression x Male NPT Elbow -
1/4 in. x 1/4 in. Compression x Female NPT Polypropylene Elbow -
1/4 in. x 1/4 in. Compression x Male Polypropylene Branch Tee -
1/4 in. x 1/8 in. Compression x Male NPT Polypropylene Adapter -
5/16 in. x 1/4 in. White Nylon Reducing Compression Union -
3/8 in. Brass Compression Union Body -
3/8 in. OD x 1/2 in. Brass Compression x Male NPT Adapter with Sleeve Nut -
3/8 in. White Nylon Bulkhead Compression Union -
3/8 in. x 1/2 in. Brass Compression x Male NPT Barstock Elbow -
3/8 in. x 1/2 in. Compression x Male NPT Polypropylene Adapter
Apex Flow Solutions stocks a complete range of brass compression fittings from Midland Industries — adapters, elbows, tees, unions, and caps in every common tubing size. All fittings are manufactured from dezincification-resistant brass and ship same-week from our inventory.
Shapes and Configurations
Adapters and connectors (straight) transition between tube sizes or from tube to male/female NPT pipe thread. Elbows make 90° direction changes without tube bending. Tees create branch connections off a main run. Unions allow in-line disconnection for service access. Caps terminate an open tube end.
Sizing Reference
Compression fittings are sized by tubing OD — not pipe size. Common sizes run from 1/8 in. to 1 in. OD. When replacing an existing fitting, measure the tube's outside diameter, not the fitting thread. See our Compression Fitting Sizing Chart for a full OD-to-fitting-size reference.
Related Technical Resources
- Compression Fitting Sizing Chart & Tube Size Reference
- NPT Thread Tightening Reference
- Brass Fitting Types and Sizes: A Complete Guide
Frequently Asked Questions
What tube materials work with brass compression fittings?
Brass compression fittings work reliably with copper, brass, and aluminum tubing, which are rigid enough for the ferrule to bite and form a permanent seal. They can also be used with certain semi-rigid plastic tubing such as nylon and HDPE, though plastic tube inserts (stiffeners) are recommended to prevent the ferrule from collapsing the tube wall under compression. Soft flexible hose (PVC, rubber, silicone) is not compatible — use hose barb fittings with a clamp for those applications instead.
Do compression fittings need Teflon tape or pipe dope?
No — compression fittings seal by the ferrule mechanically deforming against the tube OD, not by thread sealant. Applying Teflon tape or pipe dope to the compression nut threads does not improve the seal and can interfere with proper ferrule seating. The only connection that may benefit from thread sealant is the male NPT end of a compression adapter where it threads into a pipe fitting or valve — that NPT joint does need tape or dope. See our Teflon Tape vs. Pipe Dope guide for when to use each.
How do I fix a leaking compression fitting?
First, try tightening the nut an additional quarter turn — many leaks at compression fittings are simply under-tightened ferrules. If tightening stops the leak, you are done. If the fitting continues to leak after tightening, the ferrule has likely been over-compressed or the tube was cut out of round, and the fitting will need to be replaced (ferrules are single-use and cannot be re-sealed once deformed). Always cut tubing squarely, deburr the cut end, and bottom the tube into the fitting body before tightening. See our Compression Fitting Leak Troubleshooting guide for step-by-step instructions.