Overview
A brass straight fitting is an in-line connector for oil and grease lubrication systems. It joins lubrication tubing to a threaded port, or two tubes in a straight run, so feed lines run from a pump or divider valve straight to a bearing point. They come in corrosion-resistant brass, a material that tolerates lubricants and machine temperatures.
Unlike a grease nipple, which mates with a grease gun coupler, a straight fitting is a passive connection part that holds the line together within the declared limits below. If you are unsure which combination fits, send us your line details for help matching tube and thread sizes.
Technical Specifications
| Item | Declared Specification |
|---|---|
| Material | Corrosion-resistant brass |
| Working pressure | Push-in fittings: up to 60 bar; Pipe fittings: varies by size |
| Temperature | Standard: -20°C to +120°C; Hot oil applications: up to 200°C |
| Lubricant types | Oil and grease |
| Thread forms | NPT, BSP, and metric threads |
| Tube connection | Imperial and metric tube OD, tube-to-thread or tube-to-tube |
| Type | Available Sizes |
|---|---|
| Imperial tube OD | 1/8″, 1/4″, 3/8″, 1/2″, 5/8″, 3/4″, 1″ |
| Metric tube OD | 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm |
| NPT thread | 1/8″, 1/4″, 3/8″, 1/2″, 3/4″, 1″ |
| BSP thread | 1/8″, 1/4″, 3/8″, 1/2″, 3/4″, 1″ |
| Metric thread | M10x1.0, M12x1.5, M14x1.5, M16x1.5, M18x1.5, M20x1.5 |
Selection and Working Principle
The tube side grips the tubing and the thread side seals in the port. Two dimensions must be chosen separately: a 6mm x 1/4″ BSP fitting joins a 6mm tube to a 1/4″ BSP port, with the tube and thread selections independent. Measure the tube outside diameter, then identify the thread form on the port; when matching an existing line, measuring the old fitting beats guessing.
Push-in styles grip the tube internally and assemble quickly; the push-in family carries the declared 60 bar ceiling. Threaded pipe fittings seal on the thread with PTFE tape and vary in pressure by size. Standard fittings cover -20°C to +120°C; hot oil circuits should use the up-to-200°C variants.
Small-bore lubrication lines often pair these fittings with nylon tubing: see our 4mm nylon pipe for 4mm runs and 6mm nylon tubing for 6mm runs.
One rule to remember: BSP and NPT threads are not interchangeable. The profiles and pitches differ, and forcing one into the other damages the fitting and the port.
Installation and Use
For push-in styles, cut the tube square, remove burrs, and push the tube in fully until it seats; a gentle pull confirms the grip. For threaded styles, wrap the male thread with PTFE tape in the tightening direction, start by hand, then finish with a wrench. Brass is softer than steel, and over-tightening can crack the fitting or distort the port threads.
After assembly, pressurize the line normally and check each new joint. If a joint seeps, stop, depressurize, and remake it with fresh tape rather than tightening harder.
Applications
Brass straight fittings suit any lubrication line needing a straight, demountable connection:
- Centralized lubrication systems, with feed lines from a pump or divider valve to multiple points
- Machine tools, with oil or grease fed to bearings and slideways
- Injection molding machines and presses with lubrication manifolds
- Construction and agricultural machinery grease lines
- Automotive service and fleet maintenance shops
- Conveyors and industrial equipment on manual or automatic lubrication circuits
Maintenance
Inspect fittings during routine lubrication rounds: look for seepage at threads, tube movement at the grip, and damage from vibration or impact. A fitting that still seeps after retightening, or has cracked threads, should be replaced. Clean old tape off both parts and apply fresh tape on reassembly.
FAQ
What is a brass straight fitting?
An in-line brass connector for oil and grease lubrication lines, joining tubing to a threaded port or two tubes in a straight run. It is a passive connection part, not a grease nipple, and carries no check valve.
How do I choose the tube size and the thread size?
Choose them separately: measure the tube outside diameter for the tube side and identify the thread form and size on the port. When in doubt, measure the old fitting first.
Are NPT and BSP threads interchangeable?
No. Their forms and pitches differ; forcing one into the other damages the threads and seals poorly. Confirm your equipment’s form first.
Should I pick a straight fitting or an elbow fitting?
Pick a straight fitting when the run continues in one line from the port; pick an elbow when the line must turn to clear surrounding parts. Routing space decides, not sealing quality.
What pressure can a brass straight fitting handle?
Push-in styles carry the declared 60 bar ceiling; threaded pipe fittings vary by size, so check the exact size rating against your system pressure.
Can these fittings carry both oil and grease?
Yes. The declared range covers oil and grease. Standard fittings cover -20°C to +120°C, with hot oil variants up to 200°C; match fitting to fluid and temperature.
Do I need thread sealant on the threads?
Yes. We recommend PTFE tape on all threaded joints, applied in the tightening direction; it helps the joint seal and eases disassembly.
Why does my new fitting seep after installation?
Usually insufficient tape, tape against the tightening direction, or a fitting cracked by over-tightening. Depressurize, strip, inspect, and remake the joint; tightening harder rarely helps.
Can I reuse a brass fitting?
Often yes, if threads and tube grip are undamaged: replace the tape and reassemble. If it is cracked, distorted, or no longer grips, fit a new one.
Who supplies these fittings and how do I order?
They are supplied by IsoHiTech Lubrication Systems, founded in 2023, engineering since 2006; for selection help, email inquiry@isohitech.com or use our quote form with your line details.
