Lubrication Straight Coupling — Metric & PT Thread Adapters
Lubrication straight couplings join tubing, hose, or two threaded ports in line without a 90° bend. IsoHiTech lists steel straight adapters from M6 through M10 and PT / NPT pipe threads for centralized oil and grease systems.
Hub page for all coupling types: lubrication coupling solutions. Related: elbow coupling · reduce coupling.
Thread Types Explained
| Thread | Common use | Notes |
|---|---|---|
| M6 × 1 | Small injector ports, grease nipple adapters | Light oil PDI branches |
| M8 × 1 | Injector outlets, small block ports | Most common on DLX / single injectors |
| M10 × 1 | Pump outlets, larger injectors | Higher flow branches |
| PT 1/8, PT 1/4, PT 3/8 | European machine tooling | Taper pipe thread — do not mix with NPT without adapter |
| NPT 1/8, NPT 1/4 | North American equipment | Taper seal — tighten to spec only |
Sample Part Numbers on This Page
| P/N | Configuration | Typical application |
|---|---|---|
| 30073 | Female M6 × Male M6 | Extension between two M6 ports |
| 30080 | Female M8 × Male M6 | Step-down adapter |
| 30071 / 30028 | Female M8 × Male PT/NPT 1/8 | Block port to tube fitting |
| 30074 | Female M8 × Male M10×1 | Injector to pump line |
| 30019 / 30085 | Female M10 × Male PT 1/8 or 1/4 | Main line branch |
| 30157 / 30159 | Male PT/NPT 1/8 or 1/4 both ends | Pipe-to-pipe extension |
Selection Workflow
- Identify port thread on pump, injector, or block (metric vs PT vs NPT).
- Identify opposite end — tube fitting, smaller metric port, or pipe thread.
- Confirm tube OD if compression sleeve is involved (often 4 or 6 mm on secondary lines).
- Order spares: 2–3 pcs per thread size per machine for service kits.
Installation Tips
- Use correct wrench on hex body — avoid gripping compression nut with pipe wrench.
- PT/NPT joints: tighten until snug; over-torque cracks small straight bodies.
- Support tubing within 50 mm with pipe clips.
- After install, run a low-pressure prime before full system pressure.
System Pairing
- PDI circuits — DLX single injector · positive injector systems
- Progressive grease — Lincoln SSV outlet adapters on SSV divider valve page
- Tubing — pipe guide · hose catalog
- Pumps — SM air grease pump · hand grease pump
Troubleshooting
| Problem | Cause | Fix |
|---|---|---|
| Cross-thread | PT fitting into NPT port | Replace with correct thread standard |
| Creep leak | Undersized sleeve for tube OD | Match sleeve to 4/6/8 mm tube |
| Broken body | Over-torque or side load | Add clip; replace coupling |
Custom straight adapters: contact for a quote.
An inline adapter connecting two threaded ports or a port to a tube fitting without changing flow direction.
Match the larger port on your injector or pump. M8 is standard on many DLX injectors; M10 on larger pump outlets.
Only with correct conversion adapters. PT and NPT are not interchangeable despite similar sizes.
Use couplings with compression sleeve for 6 mm OD or male thread to 6 mm tube couplings (322xxx / 323xxx series).
Yes — e.g. P/N 30157 (PT 1/8) and 30159 (NPT 1/4) for pipe extensions.
Between pump outlet and main line, injector port and branch tube, and block outlet and secondary line.