A hook-on grease nipple is the locking-collar member of the grease nipple family. It keeps the standard 6.5 mm conical head and the spring-loaded ball check of a regular nipple, and adds an external hook groove that a lock-on coupler captures and holds. Any standard 4-jaw hydraulic coupler still seals on the head and pumps normally – it simply does not engage the lock. The family is mapped in the grease fitting types guide, and head and thread dimensions cross-reference the grease zerk sizes chart.
Specifications
| Item | Specification |
|---|---|
| Threads | BSPP G1/8″, G1/4″; metric M6x1.0, M8x1.25, M10x1.5; NPT 1/8″, 1/4″ optional |
| Body angles | Straight, 45°, 90° |
| Head diameter | 6.5 mm standard series; 8.0 mm reinforced hook collar, heavy-duty series |
| Working pressure | 400 bar (5,800 PSI) standard; 600 bar (8,700 PSI) heavy-duty |
| Hex sizes | Standard: M6 = 7 mm, M8 = 9 mm, M10 = 11 mm, 1/4″ = 9/16″; heavy-duty: M8 = 11 mm, M10 = 12 mm, 1/4″ = 5/8″ |
| Material | Carbon steel, zinc plated; 304 or 316 stainless optional |
| Ball check | Spring-loaded, opening pressure 5-15 bar |
| Temperature | -30°C to +100°C with NBR seal; -20°C to +200°C with FKM seal |
| Lock engagement | Sliding-sleeve, lever-release, and clip-type lock-on couplers |
How the Lock Works
Three coupler styles engage the hook groove: sliding-sleeve, lever-release, and clip-type. In each style, jaws or a sleeve close into the groove so the coupler cannot be pushed or vibrated off the head until the operator releases it. The hook sits external to the pressure path: it carries no grease pressure, and the internal ball check is unchanged from a standard nipple, opening at 5-15 bar. The heavy-duty series pairs an 8.0 mm reinforced hook collar with the same locking principle and a 600 bar working rating.
Threads, Angles, and Materials
Threads run BSPP G1/8″ and G1/4″, metric M6x1.0, M8x1.25, and M10x1.5, with NPT 1/8″ and 1/4″ optional. Bodies come straight, 45-degree, and 90-degree; angled bodies let the coupler approach square to the head on crowded points. The standard build is zinc-plated carbon steel, with 304 or 316 stainless optional for wet and marine service – the stainless steel grease nipples page covers the wider stainless range. Where no lock is needed, a single-size standard nipple such as the M8 grease nipple is the simpler choice, and long straight grease nipples cover points set deep inside guards and housings.
Clearance and Hook Geometry
The hook adds 2-4 mm to the outer diameter, and lock-on couplers run 5-8 mm longer than standard couplers. Before settling on a body angle, confirm the coupler sleeve has room to slide back for release and that the longer coupler body clears adjacent housings. On 45-degree and 90-degree models, face the hook groove toward the expected coupler approach direction.
Installation Torque
| Thread | Hex size | Steel housing | Cast iron | Aluminum |
|---|---|---|---|---|
| G1/8″ / M6 | 7 mm | 5-8 Nm | 4-7 Nm | 3-5 Nm |
| G1/4″ / M8 | 9 mm | 8-12 Nm | 7-10 Nm | 5-8 Nm |
| M10 | 11-12 mm | 12-18 Nm | 10-15 Nm | 8-12 Nm |
Use a calibrated wrench on clean threads, with a medium-strength thread sealant in steel housings; the softer-housing columns reflect lower strip strength.
What These Nipples Do Not Do
Three limits deserve plain statements. A standard coupler on a hook-on nipple works normally but never engages the lock – the feature stays unused, with no damage either way. We publish no corrosion-test hours and no vibration-retention figures for this series; if your specification calls for tested values, ask before ordering. And if a hook breaks off, the nipple keeps sealing as a plain standard nipple until replaced – the lock function is gone, the pressure path is not.
For selection, send the thread size, coupler type, and working pressure, or contact us for a quote.
Frequently Asked Questions
What is a hook-on grease nipple?
A standard grease nipple – 6.5 mm conical head and spring-loaded ball check – with an added external hook groove that a lock-on coupler captures, so the coupler stays on the head under vibration until the operator releases it.
Will a standard grease gun coupler work on it?
Yes. The 6.5 mm head and ball check are unchanged, so a standard 4-jaw hydraulic coupler seals and pumps normally; the lock simply stays unused.
What actually locks the coupler on?
The coupler, not the nipple. Sliding-sleeve, lever-release, and clip-type couplers close jaws or a sleeve into the hook groove; the nipple itself has no moving lock parts.
What happens if the hook breaks?
The nipple keeps working as a standard nipple: the ball check and pressure path are untouched. Replace the nipple when convenient to restore the locking function.
Are these the same as pin type grease nipples?
No. A pin type grease nipple presents a pin or slotted head that only a dedicated pin-type coupler engages. A hook-on nipple keeps the standard head and stays compatible with ordinary hydraulic couplers.
Which threads and angles are available?
BSPP G1/8″ and G1/4″, metric M6x1.0, M8x1.25, and M10x1.5, with NPT 1/8″ and 1/4″ optional; bodies come straight, 45-degree, and 90-degree.
What working pressure do they handle?
400 bar (5,800 PSI) in the standard series and 600 bar (8,700 PSI) in the heavy-duty series with the reinforced hook collar.
Is stainless available for marine service?
Yes. 304 or 316 stainless builds are optional across the thread range for wet and marine environments; the standard build is zinc-plated carbon steel.
How much clearance does the locking coupler need?
The hook adds 2-4 mm to the outer diameter, and lock-on couplers run 5-8 mm longer than standard couplers; also leave room for the sleeve to slide back on release.
Related Pages
- Grease fitting types guide
- Grease zerk sizes chart
- M8 grease nipple
- Long straight grease nipple
- Stainless steel grease nipples
- Pin type grease nipple
Hook-on for locking duty, pin type for dedicated couplers, stainless for corrosion resistance – or contact us for a quote with your thread and coupler details.
