For ACR copper used with compression fittings (might also be called press by some manufacturers, like Vulkan Lokring), press fittings (like RLS/ZoomLock) and push-to-connect fittings （like ZPUSH）, the outside diameter (OD) tolerance of the copper tube is critical so the O-ring seals correctly. Most manufacturers base their requirements on ASTM International standards, primarily ASTM B280 and sometimes ASTM B88 when approved.
Below is a typical OD size and tolerance table used for compression, press and push-to-connect ACR fittings. (Values reflect common tolerances from ASTM B280 and fitting manufacturers.)
LWC copper tubes
Copper Tube OD Size & Tolerance for Press / Push-to-Connect Fittings
| Nominal ACR Size | Actual OD (in.) | OD Tolerance (± in.) | Typical Use |
| 1/4" | 0.25 | ±0.003 | Mini splits, capillary lines |
| 3/8" | 0.375 | ±0.003 | Small refrigeration |
| 1/2" | 0.5 | ±0.003 | Residential HVAC |
| 5/8" | 0.625 | ±0.003 | Liquid lines |
| 3/4" | 0.75 | ±0.003 | HVAC piping |
| 7/8" | 0.875 | ±0.003 | Suction lines |
| 1-1/8" | 1.125 | ±0.004 | Commercial HVAC |
| 1-3/8" | 1.375 | ±0.004 | Larger refrigeration |
| 1-5/8" | 1.625 | ±0.004 | VRF / refrigeration |
| 2-1/8" | 2.125 | ±0.005 | Commercial systems |
| 2-5/8" | 2.625 | ±0.005 | Large suction lines |
| 3-1/8" | 3.125 | ±0.006 | Industrial refrigeration |
| 3-5/8" | 3.625 | ±0.006 | Industrial refrigeration |
| 4-1/8" | 4.125 | ±0.008 | Large HVAC systems |
ACR copper tube
Important Notes for Flameless Fittings
1. Roundness requirement
· Tubing must be within OD tolerance and not ovalized.
2. Surface condition
· No deep scratches where the O-ring seals.
3. Tube types typically accepted
· ACR tubing meeting ASTM B280
· Some manufacturers allow Type L from ASTM B88 if cleaned for refrigeration.
4. Tube preparation
· Deburr
· Calibrate if out of round
· Clean surface
Conclusion: Choose Stability, Choose Scottfrio
| Fitting Type | OD Tolerance Sensitivity | Notes |
| Press fittings | Medium | Press tool compensates slightly |
| Push-to-connect | High | OD must be very accurate |
| Compression ACR | Highest | ID & OD must be both within tolerance requirement |
Push-to-connect fittings are usually more sensitive to OD tolerance than press fittings, while compression fittings require high accuracy for both ID and OD due to the structure.
There are detailed tube OD tolerance requirements published for VULKAN Lokring fittings, but ZPUSH push-to-connect fittings typically follow the same OD tolerance ranges as standard ACR tubing (ASTM B280) because the O-ring sealing requires a precise OD. Below is a combined engineering reference table based on manufacturer installation manuals and technical documents.
Vulkan Lokring fitting
1. Tube OD Tolerance — Vulkan Lokring Fittings
Lokring compression-type connectors require the copper tube OD to stay within a specific range so the radial compression rings create the metal-to-metal seal. VULKAN Lokring installation tables specify the allowable OD range for each tube size.
| Tube Size | Nominal OD | Minimum OD | Maximum OD | OD Tolerance |
| 1/4 in | 0.250 in | 0.246 | 0.254 | ±0.004 |
| 3/8 in | 0.375 in | 0.371 | 0.379 | ±0.004 |
| 1/2 in | 0.500 in | 0.496 | 0.504 | ±0.004 |
| 5/8 in | 0.625 in | 0.621 | 0.629 | ±0.004 |
| 3/4 in | 0.750 in | 0.746 | 0.754 | ±0.004 |
| 7/8 in | 0.875 in | 0.871 | 0.879 | ±0.004 |
| 1 in | 1.000 in | 0.994 | 1.006 | ±0.006 |
| 1-1/4 in | 1.250 in | 1.244 | 1.256 | ±0.006 |
| 1-1/2 in | 1.500 in | 1.494 | 1.506 | ±0.006 |
| 2 in | 2.000 in | 1.99 | 2.01 | ±0.010 |
Additional Lokring requirements
· Tube diameter range typically 6 mm – 41.3 mm (1/4″–1-5/8″) depending on fitting type.
· Minimum copper wall thickness: ≈0.7 mm for HVAC systems.
· Tube must be hard drawn (not annealed) for some applications.
ZPUSH fitting
2. Tube Requirements — ZPUSH Push-to-Connect Fittings
For ZPUSH HVAC push fittings, manufacturers generally require:
Copper tube standard
· ASTM B280 (ACR refrigeration tube)
· Some allow ASTM B88 Type L if OD tolerance is maintained.
Typical OD tolerance required for O-ring seal
3. Comparison of Tube Tolerance Requirements
| Tube Size | Nominal OD | Acceptable OD Range | Approx Tolerance |
| 1/4 in | 0.25 | 0.247 – 0.253 | ±0.003 |
| 3/8 in | 0.375 | 0.372 – 0.378 | ±0.003 |
| 1/2 in | 0.5 | 0.497 – 0.503 | ±0.003 |
| 5/8 in | 0.625 | 0.622 – 0.628 | ±0.003 |
| 3/4 in | 0.75 | 0.747 – 0.753 | ±0.003 |
| 7/8 in | 0.875 | 0.872 – 0.878 | ±0.003 |
| 1-1/8 in | 1.125 | 1.121 – 1.129 | ±0.004 |
Additional push-fit requirements
· Tube must be round within ~0.002–0.004 in
· Surface scratches must be less than ~0.005 in deep in the sealing area
· Tube must be deburred and cleaned before insertion.
Push fittings are more sensitive to OD variation than Lokring because they rely on O-ring compression rather than metal deformation.
Copper tube
3. Comparison of Tube Tolerance Requirements
| Feature | Lokring | ZPUSH |
| Sealing method | Metal compression rings | O-ring seal |
| OD tolerance sensitivity | Medium | High |
| Typical tolerance | ±0.004–0.006 in | ±0.003–0.004 in |
| Tube hardness | Often hard drawn required | Annealed acceptable |
| Tube standards | ASTM B280 / B88 | ASTM B280 primarily |
What do you know about ZPUSH fittings?
ZPUSH fittings are part of a newer category of flameless HVAC refrigerant fittings known as push-to-connect (push-fit) fittings. They are designed to connect refrigerant copper lines without brazing, flaring, or pressing tools.
Here’s a clear breakdown of what they are and how they work.
What ZPUSH Fittings Are
ZPUSH refers to push-to-connect HVAC refrigerant fittings that allow technicians to join copper refrigerant lines simply by pushing the tube into the fitting body.
The concept is similar to other HVAC push systems such as ZoomLock PUSH, but each manufacturer has its own internal sealing and locking design.
Key concept:
· Tool-free connection
· No flame or brazing required
· Removable using a release tool
Push-to-connect HVAC fittings in general are intended to make installation faster and safer, especially in buildings where open flames are restricted. 
ZPUSH installation
How ZPUSH / Push Refrigerant Fittings Work
Internally, the fitting typically has three main components:
1.Grip ring (stainless steel teeth)
· Bites into the copper tube to hold it in place.
2.O-ring seals (usually double O-ring)
· Creates the refrigerant-tight seal around the tube OD.
3.Tube stop
· Ensures the tube is inserted to the correct depth.
When the tube is pushed in:
· The grip ring locks the pipe.
· The O-rings seal against the tube OD.
· The connection becomes pressure-tight.
Many designs use double O-rings plus a mechanical grip ring to resist vibration and pressure.
Typical Applications
Push HVAC fittings like ZPUSH are used in:
· Mini-split installations
· Residential air-conditioning
· Refrigeration service repairs
· Retrofit work where brazing is difficult
· Areas requiring no open flame permits
They can connect:
· ACR copper tubing
· Some coated aluminum line sets
Typical Technical Performance (for HVAC push fittings)
Typical values for this class of fittings:
These ranges match many push-type refrigerant fittings used in HVAC systems.
| Parameter | Typical Value |
| Pressure rating | ~700 psi |
| Temperature | −40°F to 250°F |
| Tube sizes | 1/4" – 7/8" OD |
| Tubing standard | ASTM B280 ACR copper |
| Seal material | HNBR or similar refrigerant-rated elastomer |
Advantages
1. No brazing
· Eliminates flame risk.
2. Faster installation
· Connections can be made in seconds.
3. No nitrogen purge required
· Because there is no heat applied.
4. Removable
· Some models allow disassembly with a release clip.
Limitations
Technicians often point out several practical considerations:
· Tube preparation is critical (deburring, cleaning).
· OD tolerance must be precise (ACR tubing).
· O-rings introduce a long-term aging risk compared with brazed joints.
· Some OEM equipment does not approve push fittings on factory connections.
How ZPUSH Fits in the Flameless Fitting Market
There are three major categories of flameless HVAC fittings:
Push fittings are generally the fastest installation method, but also the most sensitive to tube OD tolerance and surface condition.
| Type | Example Systems | Connection Method |
| Press fittings | ZoomLock / RLS | Tool presses copper onto O-ring |
| Compression fittings | Vulkan Lokring | Metal deformation seal |
| Push-to-connect | ZPUSH / ZoomLock PUSH | Grip ring + O-ring |
Push fittings are generally the fastest installation method, but also the most sensitive to tube OD tolerance and surface condition.
Table of Contents >
- 1. Copper Tube OD Size & Tolerance for Press / Push-to-Connect Fittings
- 2. Important Notes for Flameless Fittings
- 3. Conclusion: Choose Stability, Choose Scottfrio
- 4. What do you know about ZPUSH fittings?
- 5. How ZPUSH / Push Refrigerant Fittings Work
- 6. How ZPUSH Fits in the Flameless Fitting Market