Press Fitting Technical Specifications
Press joining replaces solder, thread and glue with a mechanical seal: the fitting is slipped over prepared pipe and a jaw compresses the fitting body onto it, trapping an elastomeric O-ring in a permanent, leak-tight joint. No flame, no flux, no cutting oil, no draining the line dry. This page collects the dimensional and material data you need to specify and install a press system correctly.
How the joint works
Every press joint has three elements, and all three have to be right:
- The pipe must be cut square, deburred inside and out, and free of scoring in the seal zone. A longitudinal scratch under the O-ring is the most common cause of a joint that passes a quick pressure test and weeps later.
- The insertion depth must be full. Mark the tube from the fitting's stop before assembly and check the mark after pressing. A shallow insertion presses cleanly and does not seal — the crimp forms on the wrong part of the tube.
- The jaw profile must match the fitting system. Press profiles are proprietary and are not interchangeable between manufacturers, even at identical nominal size. A mismatched jaw will close and will leave a joint that is not to specification.
Most systems include a feature that leaks deliberately if the joint is left unpressed during a pressure test, so an unpressed connection is found on test rather than in service. Do not treat that as a substitute for tracking which joints you have pressed.
Copper tube dimensions (ASTM B88)
Press fittings for potable water and hydronic service are sized to copper tube size (CTS). Outside diameter is the nominal size plus 1/8 inch — the number stamped on the fitting is the nominal size, not the OD.
| Nominal | OD (in) | Wall — Type K | Wall — Type L | Wall — Type M |
|---|---|---|---|---|
| 1/2" | 0.625 | 0.049 | 0.040 | 0.028 |
| 3/4" | 0.875 | 0.065 | 0.045 | 0.032 |
| 1" | 1.125 | 0.065 | 0.050 | 0.035 |
| 1-1/4" | 1.375 | 0.065 | 0.055 | 0.042 |
| 1-1/2" | 1.625 | 0.072 | 0.060 | 0.049 |
| 2" | 2.125 | 0.083 | 0.070 | 0.058 |
| 2-1/2" | 2.625 | 0.095 | 0.080 | 0.065 |
| 3" | 3.125 | 0.109 | 0.090 | 0.072 |
| 4" | 4.125 | 0.134 | 0.110 | 0.095 |
Wall thicknesses in inches. Type K is heaviest, then L, then M. Press fittings seal on the outside diameter, which is identical across all three types — so a press fitting that fits Type L fits Type K and Type M of the same nominal size. Local code, not the fitting, decides which type is permitted for a given application.
Seal materials — the choice that is not interchangeable
The O-ring compound defines what the fitting may carry. Fittings are colour-coded by manufacturer, but colour conventions differ between brands, so read the marking on the fitting rather than trusting the colour alone.
| Compound | Typical service | Never use for |
|---|---|---|
| EPDM | Potable water, hydronic heating and chilled water, compressed air (oil-free) | Fuel gas, fuel oil, refrigerant, any hydrocarbon — EPDM swells and degrades |
| HNBR | Fuel gas, propane, fuel oil, refrigerant lines, oil-bearing compressed air | Applications where the fitting is not separately listed for that service |
| FKM (fluoroelastomer) | Elevated temperature and aggressive-media service, where the manufacturer offers it | Substituting into a system not rated for it |
A gas-rated fitting and a water-rated fitting of the same size and brand can look nearly identical on the shelf. Confirm the fitting is marked for the service before it goes in the wall.
Press systems by material
| System | Pipe it joins | Typical use |
|---|---|---|
| Copper press (CTS) | Copper tube to ASTM B88, Types K, L and M | Potable water, hydronic, chilled water |
| Carbon steel press | Black and galvanized steel pipe to ASTM A53, Schedule 5 through 40 | Hydronic, fire protection, compressed air, industrial |
| Carbon steel press — gas | Steel pipe to ASTM A53, gas-rated seal | Fuel gas distribution, listed to ANSI LC 4 / CSA 6.32 |
| Stainless press | 304 and 316 stainless tube and pipe | Corrosive media, food and beverage, high-purity, marine |
| ACR press | ACR copper tube to ASTM B280 | Refrigerant lines in air conditioning and refrigeration |
Governing standards
- ASME B16.51 — Copper and copper alloy press-connect pressure fittings. Dimensions, materials and performance for copper press.
- ASTM B88 — Seamless copper water tube (Types K, L, M).
- ASTM B280 — Seamless copper tube for air conditioning and refrigeration field service (ACR).
- ASTM A53 — Welded and seamless black and hot-dipped galvanized steel pipe.
- ANSI LC 4 / CSA 6.32 — Press-connect metallic fittings for use in fuel gas distribution systems.
- NSF/ANSI 61 — Drinking water system components, health effects.
- NSF/ANSI 372 — Lead content evaluation, for compliance with the U.S. lead-free requirement (weighted average of 0.25% lead or less on wetted surfaces).
Tools and jaws
The press tool supplies the force and controls the cycle; the jaw determines what the tool can actually join.
- Profiles are proprietary. Match the jaw to the fitting manufacturer's system. A jaw that physically closes on another brand's fitting does not produce a joint to that manufacturer's specification.
- Capacity is set by force rating. Standard press tools typically cover copper up to 2 inches. Above that — and on stainless and heavier steel — fixed jaws give way to rings driven by an actuator: the ring wraps the fitting and the actuator closes it, which is what makes large-diameter pressing possible where a fixed jaw could never swing.
- Compact and short-throw tools trade capacity for access in joist bays and tight mechanical rooms.
- Jaws are consumables. The profile wears. A worn jaw produces joints that look pressed and hold on test but fail later; manufacturers publish an inspection interval by cycle count.
- Tools require periodic factory calibration. Most log cycle counts and lock out when service is due. That is a maintenance obligation, not a defect.
- Check tool generation, not just brand. Jaw mounting has changed across press tool generations, and a current jaw does not always fit an older tool.
Installation checklist
- Cut the pipe square with a tube cutter or a wheel cutter suited to the material. Do not use an abrasive wheel on copper.
- Deburr inside and out. A burr can roll the O-ring out of its groove on insertion.
- Inspect the seal zone. Reject any length with a longitudinal scratch, deep tool mark or out-of-round section in the area the O-ring will sit on.
- Confirm the O-ring is present and seated. A missing or displaced O-ring is a leak that will pressure-test intermittently.
- Mark the insertion depth on the pipe from the fitting stop.
- Insert to the mark, seat the jaw square to the fitting, and press one full cycle.
- Verify the mark after pressing, and confirm the jaw left a complete impression around the full circumference.
- Respect the manufacturer's minimum distance between adjacent joints and between a joint and a bend — the jaw needs clearance to seat square.
Pressure and temperature ratings
Working pressure and temperature limits are set by the individual system, not by press as a method: they vary by manufacturer, by material, by size and by seal compound, and gas service is further limited by code irrespective of what the fitting is rated for. Always specify against the current submittal sheet for the exact fitting you are installing, and confirm the local code authority permits press for that application.
If you need a submittal or a compatibility answer for something we stock, our team can pull it — reach us at +1 (623) 307-5144 or info@thehousesupplier.com.