1/8 in Straight 316 Stainless Steel Grease Nipple
This page covers the 1/8 in straight grease nipple in 316 stainless steel: imperial taper pipe thread, hydraulic-type conical head. Two thread forms share one body: 1/8″ BSPT (R/RC, 28 TPI, 55° thread angle) or 1/8″-27 PTF (60° thread angle, 1:16 taper). Other styles sit in our lubrication fitting category.
Choosing Between BSPT and PTF
BSPT is the form most often found on European and Asian machinery, with 28 TPI and a 55° thread angle. PTF is most often found on North American equipment, with 27 threads per inch, a 60° angle, and a 1:16 taper. Both male threads measure roughly 10 mm across the major diameter; diameter alone cannot separate them.
Material and Head
The body is 316 stainless steel (UNS S31600), passivated, with 2 – 3% molybdenum for wet, chloride-bearing exposure. The 6.5 mm hydraulic-type conical head follows DIN 71412 geometry at 550 HV or higher, so standard coupler jaws seat on it.
| Thread | 1/8″ BSPT (R/RC, 28 TPI, 55° thread angle) or 1/8″-27 PTF (60° thread angle, 1:16 taper) |
| Material | 316 stainless steel (UNS S31600), passivated; 2 – 3% molybdenum |
| Head | Hydraulic-type conical head, 6.5 mm diameter (DIN 71412 compatible); 550 HV or higher |
| Overall length | 15 – 16 mm |
| Thread length | 5.5 – 6.5 mm |
| Hex across flats | 11 mm |
| Bore | 1.5 mm |
| Max working pressure | 8,000 PSI (551 bar) |
| Proof pressure | 12,000 PSI (827 bar) |
| Ball check valve | FKM seal + 316 stainless spring; opening pressure 5 – 15 bar |
| Temperature range | -60°C to +200°C (FKM seal limit); short-term peak +220°C; above +150°C continuous, shorten seal inspection intervals |
| Install torque | 8 – 12 Nm recommended; steel housing max 15 Nm; aluminum housing reduce 30% |
| Interchange standards | DIN 71412 |
Pressure and Temperature
Max working pressure is 8,000 PSI (551 bar). The 12,000 PSI (827 bar) proof pressure is a verification figure 1.5x the working rating (12,000 / 8,000 = 1.5), not a service target. The ball check opens at 5 – 15 bar and reseats behind an FKM seal. Continuous service spans -60°C to +200°C, +220°C short-term peak; above +150°C continuous, shorten seal inspection intervals.
Applications and Boundaries
This straight nipple suits machine tools, conveyors, bearing housings, agricultural machinery, construction machinery chassis, and factory automation with imperial threads. For very high flow, a giant button head high-flow fitting is the better concept; for cramped corners, 45° or 90° elbow nipples give angled access.
- 1/8 BSPT and 1/8-27 PTF are both about 10 mm across the major diameter but not interchangeable; the wrong thread damages the female port.
- 316 threaded into a 316 stainless hole carries a galling risk; use a compatible thread lubricant or anti-seize and control torque.
- The FKM seal stops at -60°C to +200°C, +220°C short-term peak; beyond that, a different seal option must be confirmed when ordering.
Still unsure? Request a quotation with a photo of the old fitting.
Frequently Asked Questions
How do I choose between BSPT and PTF for a 1/8 in nipple?
Route by equipment origin: European and Asian machinery usually takes the 55° BSPT form, North American equipment the 60° dryseal PTF form. They sit close in size, so never force a nipple that resists; measure to confirm.
How do I measure an unknown thread in the field?
Start with a pitch gauge: 0.907 mm points to 28 TPI BSPT, 0.941 mm to 27 TPI PTF. Then check the flank angle, 55° versus 60°, and the taper. A diameter near 10 mm is only a cross-check; it cannot separate the two forms.
M10 x 1 and 1/8 BSPT both sit near 10 mm: how to tell them apart
Measure pitch: M10 x 1 runs 1.00 mm and stays parallel; 1/8 BSPT runs 0.907 mm with a visible taper. A metric result routes to the M10 x 1 grease nipple page.
When should I choose 316 stainless over zinc plated carbon steel?
Pick 316 stainless steel for rain, humidity, washdown, or chloride-bearing atmospheres; its 2 – 3% molybdenum helps resist pitting. In dry indoor conditions, zinc plated carbon steel is usually enough.
What coupler fits the 6.5 mm conical head?
A standard four-jaw hydraulic coupler seats on the 6.5 mm conical head. Near the 8,000 PSI ceiling, a four-jaw grease coupler built for high pressure is the matching accessory.
What does the 5 – 15 bar opening pressure do?
The ball stays seated until line pressure reaches 5 – 15 bar, so pumped grease moves toward the bearing, not back out of the nipple. At rest, the FKM seal keeps dust and grit out of the bore.
What torque should I use during installation?
Use 8 – 12 Nm; do not exceed 15 Nm in a steel housing. In aluminum, reduce by 30%: 30% of 8 – 12 Nm is 2.4 – 3.6 Nm, landing near 5.6 – 8.4 Nm. An 11 mm wrench fits the hex. Stop at a firm seat; extra turns raise galling risk.
Do I need thread sealant on the taper thread?
A taper thread seals by wedging, so a sound thread can seal without compound. Many installers add sealant or thread tape as an aid. On stainless-to-stainless joints, a compatible anti-seize product also limits galling.
What does the 12,000 PSI proof pressure mean?
It is a verification figure, not a service pressure: the working ceiling stays 8,000 PSI (551 bar), and proof sits 1.5x above it (12,000 / 8,000 = 1.5). Size to the working figure.
Who supplies this 1/8 in stainless grease nipple?
IsoHiTech Lubrication Systems, founded in 2023, engineering since 2006, supplies this nipple alongside the rest of the range. For drawings, seal options, or thread identification, email inquiry@isohitech.com or ask for a quote through the contact page.
