Stainless Steel Grease Nipples
Stainless steel grease nipples (also called grease fittings, Zerk fittings, or Alemite fittings) are threaded lubrication access points that allow grease to be injected into a bearing housing, pivot, or lubrication cavity using a grease gun coupler. An integrated spring-loaded steel ball check valve opens under grease gun pressure to admit lubricant and automatically seals when the gun is removed, preventing grease backflow and blocking contaminant ingress between service intervals.
The stainless steel construction makes these fittings the correct choice for environments where standard zinc-plated carbon steel fittings would corrode — marine equipment, food processing machinery, chemical plant, offshore installations, and outdoor equipment in coastal or high-humidity locations.
Stainless Steel Grade Selection
| Grade | Composition | Corrosion Resistance | Best For |
|---|---|---|---|
| 303 | 18% Cr, 8% Ni, free-machining sulphur addition | Good — passive oxide layer; not for chloride environments | General industrial, indoor applications where carbon steel is insufficient |
| 304 | 18% Cr, 8% Ni (no sulphur) | Better than 303 — improved weld and corrosion performance | Outdoor equipment, wash-down environments, moderate chemical exposure |
| 316 | 16% Cr, 10% Ni, 2% Mo | Excellent — molybdenum addition resists chloride pitting | Marine, offshore, food processing, pharmaceutical, coastal installations |
Surface finish options for 316 stainless:
- Standard passivated — chemical treatment removes free iron from the surface, enhancing the passive oxide layer; standard for most industrial applications
- Electropolished — electrochemical surface smoothing to Ra ≤ 0.8μm; required for food-grade (NSF H1) and pharmaceutical installations where surface roughness must be minimised to prevent bacterial adhesion
Technical Specifications
Performance Parameters
| Parameter | Specification |
|---|---|
| Maximum Working Pressure | 100 bar (1,450 PSI) |
| Operating Temperature | −40°C to +120°C (standard spring steel ball) / up to +204°C (stainless steel ball option) |
| Check Ball Mechanism | Spring-loaded steel ball — opens under grease gun pressure, seals automatically on disconnection |
| Check Valve Cycle Life | 10,000+ operations per SAE J534 |
| Salt Spray Resistance (SS316) | 500+ hours per ASTM B117 |
| Standards Compliance | SAE J534, DIN 71412 |
Available Thread Standards
Metric threads:
- M6×1.0, M8×1.0, M8×1.25, M10×1.0, M10×1.5, M12×1.5
SAE/Imperial threads (UNF):
- 1/4″-28 UNF (most common North American automotive standard)
- 5/16″-32 UNF
- 3/8″-24 UNF (heavy-duty applications)
British standard threads:
- 1/8″ BSPT (tapered)
- 1/4″ BSPT (tapered)
- G1/8″ ISO 228 (parallel)
Fitting Angle Options
| Angle | Description | Best For |
|---|---|---|
| Straight (0°) | Grease gun approaches axially, directly in line with the thread | Open access locations with unrestricted front clearance |
| 45° | Angled head provides intermediate approach angle | Partial front obstruction — some clearance available but straight fitting would foul adjacent components |
| 90° | Head perpendicular to thread axis — grease gun approaches from the side | Direct front access completely blocked by housing, bracket, or adjacent machinery |
| Button-head | Low-profile flat head requiring a button-head coupler rather than standard hydraulic coupler | Locations where a protruding nipple head would be a snagging hazard or would contact rotating components; automated lubrication systems |
How to Select the Correct Fitting
Step 1 — Identify the thread. Check the tapped hole in the bearing housing or component. Use a thread gauge to confirm thread form (metric, UNF, or BSPT) and pitch. Metric and UNF threads are not interchangeable. BSPT (tapered) and BSP parallel (G-thread) are also not directly interchangeable — confirm whether the port requires a tapered or parallel thread.
Step 2 — Select the grade. For indoor industrial or general automotive use, 303 or 304 is adequate and more cost-effective than 316. For marine, coastal, food processing, offshore, or chemical environments, specify 316. For food-grade or pharmaceutical applications, specify 316 with electropolished finish and confirm lubricant is NSF H1 rated.
Step 3 — Select the angle. Straight is the default. Specify 45° or 90° only when surrounding structure prevents direct grease gun access to a straight fitting. Button-head requires a matching button-head grease gun coupler — confirm the maintenance team has the correct coupler before specifying button-head fittings across a machine.
Step 4 — Confirm clearance. Angled fittings require different clearance dimensions than straight fittings. A 90° fitting requires less front clearance but needs side clearance for the gun coupler approach. Verify actual space available before finalising the angle selection.
Typical Applications
- Marine and offshore equipment — deck winches, anchor windlass bearings, steering gear lubrication points, and crane slew ring fittings on vessels and offshore platforms; 316 stainless is mandatory for salt water exposure
- Food and beverage processing — conveyor chain bearings, mixer shaft housings, and packaging machine pivot points; 316 electropolished with NSF H1 compatible grease for food-contact zone equipment
- Chemical processing plants — pump bearing housings, agitator shaft lubrication, and valve actuator bearings in environments with acid mist, solvent vapour, or caustic wash-down
- Pharmaceutical manufacturing — clean-room compatible 316 electropolished fittings on filling line and tablet press bearing points where particulate contamination from corroding fittings is unacceptable
- Coastal and outdoor construction equipment — excavator pins, crane sheaves, and compactor bearings in high-humidity coastal environments where carbon steel fittings rust rapidly between service intervals
- Agricultural machinery — seasonal equipment stored outdoors between uses; stainless fittings remain functional and corrosion-free through extended outdoor storage periods
Installation
- Thread preparation — clean the tapped port with a thread chaser; inspect for damage or cross-threading before installing the fitting
- Thread sealant — apply PTFE tape (2–3 wraps) or anaerobic pipe compound to the male thread; do not apply to the first thread to prevent sealant from entering the grease passage and contaminating the check valve
- Tightening — thread in hand-tight, then use an appropriate hex key or wrench to reach the recommended installation torque for the thread size (see table below); do not over-tighten stainless fittings into aluminium or cast iron housings — stainless-to-softer-metal thread engagement requires careful torque control to prevent galling
- Angle orientation — for angled fittings, plan the final head orientation before tightening; the head direction is set during installation and cannot be adjusted without removing and reinstalling the fitting
- Verify operation — connect the grease gun and apply one stroke; confirm grease flows through the fitting and the check valve seals (no grease weeping from the head when the gun is removed)
Installation Torque Reference
| Thread Size | Recommended Torque |
|---|---|
| M6×1.0 | 8–12 Nm |
| M8×1.25 | 15–20 Nm |
| M10×1.5 | 20–25 Nm |
| 1/4″-28 UNF | 20–27 Nm (15–20 ft-lb) |
| 1/8″ BSPT | 10–15 Nm |
FAQ
When should I use 316 stainless instead of 304?
Specify 316 when the fitting will be exposed to salt water, salt air, chlorinated cleaning agents, or acidic/alkaline chemical environments. The 2% molybdenum in 316 prevents the chloride-induced pitting corrosion that affects 304 and 303 in these conditions. For purely indoor industrial applications without chemical exposure, 304 provides adequate corrosion resistance at lower cost. 303 is the most machinable grade but has lower corrosion resistance than 304 due to its sulphur content — use 303 only for general indoor applications where precision machining is more important than maximum corrosion resistance.
Are stainless steel grease nipples compatible with standard grease gun couplers?
Yes. Stainless steel grease nipples (straight, 45°, and 90° styles) use the same head geometry as standard carbon steel fittings and are compatible with all standard hydraulic (push-on lever) grease gun couplers per DIN and SAE coupler standards. Button-head fittings require a dedicated button-head coupler — standard hydraulic couplers will not seat correctly on a button-head fitting.
Can I replace corroded carbon steel fittings with stainless steel directly?
Yes, provided the thread type and size match. Stainless steel fittings are dimensionally identical to carbon steel equivalents in the same thread standard. Remove the old fitting, clean the port thread, and install the stainless replacement using the correct torque. The only precaution is thread galling — stainless-to-stainless thread engagement (if the housing is also stainless) can gall; apply anti-seize compound to the threads in this case.
What grease types are compatible with stainless steel grease nipples?
All standard grease formulations are compatible with the stainless steel body — lithium, calcium, polyurea, and aluminium complex thickened greases, as well as synthetic and biodegradable formulations. For food-grade applications, confirm the grease is NSF H1 rated in addition to specifying the 316 electropolished fitting. For very high-temperature applications (above +120°C), specify the stainless steel ball check valve option — the standard carbon spring steel ball can lose spring tension above this temperature.
How do I know if a fitting is blocked?
A blocked fitting produces unusually high resistance when the grease gun trigger is squeezed — the gun handle requires excessive force and no grease enters the bearing. Do not continue applying high pressure, as this risks damaging the gun coupler, the fitting thread, or the bearing seal. Remove the fitting and inspect the check ball passage for contamination or corrosion. Stainless steel fittings rarely block from internal corrosion, but grease contaminated with metal particles or hardened old grease can block the ball valve seat. Replace rather than attempting to clean a blocked fitting.
Ordering information: specify grade (303, 304, or 316), surface finish (standard passivated or electropolished), angle (straight, 45°, 90°, or button-head), and thread size and standard (metric, UNF, or BSPT). Contact us for EXW Nanjing unit pricing and pack quantities.
Related lubrication resources
Grease pump systems · Air grease pump · Grease line tubing guide
Before you buy: read our grease fitting types guide.
