Quick Answer: The most common industrial Zerk fitting sizes are 1/4″-28 UNF (North America) and M6x1.0 / M10x1.5 (Europe and Asia). For tapered pipe ports, 1/8″ NPT and 1/16″ NPT are standard. The IsoHiTech straight Zerk range covers M5 through M12 and 1/4″-28 UNF with an 8,000 PSI (550 bar) carbon-steel rating.
Related: grease fitting types guide · grease gun coupler selection · grease zerk terminology
IsoHiTech supplies aftermarket-compatible lubrication components. Brand names such as Lincoln, SKF, Graco, Bijur, DropsA, Alemite, Vogel, and Delimon are used for compatibility reference only. IsoHiTech is not an authorized OEM dealer of these brands.
By type: straight (standard) – 45 and 90 degree angled – button-head / flush – extended/recessed.
What Is a Grease Zerk Fitting?
Machinery manuals refer to these points as grease ports, grease nipples, Zerks, or lubrication points — all describe the same spring-loaded check-valve fitting that lets a grease gun in and keeps dirt out.
Also referred to as grease nipple sizes when discussing port dimensions, Zerk fittings come in SAE, metric, and BSP thread standards. The most common grease nipple size is 1/4″-28 UNF in North America and M6×1.0 in European equipment.
A Zerk fitting, also called a grease fitting, grease nipple, or Alemite fitting, is a spring-loaded check valve that lets grease enter a bearing or bushing while keeping contaminants out. When the grease gun coupler presses against the ball, the ball retracts; when pressure is removed, the spring returns the ball to its seat. Choosing the correct Zerk size means matching the port thread, head geometry, and material to the application.
IsoHiTech manufactures Zerk fittings in SAE, metric, and BSP threads from carbon steel, stainless 316, and brass, rated up to 8,000 PSI (550 bar).
Grease Nipple (Zerk) Size Chart
| Thread Size | Thread Type | Hex Width | Overall Length | Common Use |
|---|---|---|---|---|
| 1/16″-27 NPT | Tapered pipe | 8 mm | 0.50″ (12.7 mm) | Small hydraulic components, compact ports |
| 1/8″-27 NPT | Tapered pipe | 11 mm | ~18 mm | Pipe-thread lubrication points |
| 1/4″-28 UNF | Straight machine | 8 mm | 14 mm | North American automotive / industrial |
| G1/8 (1/8″ BSPP) | Parallel British pipe | 14 mm | ~16 mm | UK/commonwealth equipment, marine |
| M5 x 0.8 | Metric fine | 7 mm | 12 mm | Compact accessories, small bearings |
| M6 x 1.0 | Metric | 8 mm | 14 mm | Standard automotive and light industrial |
| M8 x 1.25 | Metric | 10 mm | 16 mm | Construction and mobile equipment |
| M10 x 1.5 | Metric | 11 mm | 18 mm | High-pressure industrial systems |
| M12 x 1.25 | Metric fine | 13 mm | 20 mm | Heavy machinery, large bearings, hydraulic equipment |
Zerk Fitting Types by Shape
Straight Zerk Fittings
Straight fittings are the default for open, easy-to-reach grease points. The IsoHiTech straight grease fitting range includes M5x0.8 through M12x1.25 and 1/4″-28 UNF, rated to 8,000 PSI (550 bar) in carbon steel and available in stainless steel and brass. Each fitting has a spring-loaded ball check valve and complies with DIN 71412, ISO 6392, and ISO 3799.
45 and 90 Degree Angle Zerk Fittings
Angled nipples route the grease gun away from guards, frames, or rotating parts. The IsoHiTech angled grease nipple line offers 45 and 90 degree bodies in M5-M10 and imperial threads, with angle accuracy held to +/-2 degrees. Carbon-steel versions reach 8,000 PSI (550 bar); brass versions are rated to 3,000 PSI (207 bar) for marine or corrosive environments.
Low-Profile / Flush-Mount Fittings
Flush-mount or button-head fittings sit closer to the surface to avoid physical damage. They are common on mining buckets, compactors, and any application where protruding fittings would be sheared off. The IsoHiTech 1/16″ NPT Zerk is available in button-head style, with a 0.31″ head diameter and 1.0″ minimum clearance.
Extended Zerk Fittings
Extended nipples raise the grease point above a housing or shield, making it easier to reach with a grease gun. They are often paired with grease nipple extensions when the standard fitting is still too recessed.
How to Measure Zerk Fitting Thread Size
- Count threads per inch (TPI) with a thread gauge or caliper. 1/4″-28 UNF has 28 threads per inch; 1/8″ NPT has 27 threads per inch.
- Measure the major diameter. Use calipers across the outside of the threads. M6 measures ~6 mm; 1/4″-28 measures ~6.35 mm (0.250″).
- Check for taper. NPT threads are tapered and seal by thread deformation; UNF and metric threads are straight and may use a gasket or O-ring. BSPP (parallel) requires a bonded seal or O-ring.
- Match the hex size. The installation hex often confirms the size: M6 uses 8 mm, M8 uses 10 mm, M10 uses 11 mm, M12 uses 13 mm.
Zerk Fitting Materials: Steel vs Brass vs Stainless Steel
| Material | Working Pressure | Temp Range | Best For |
|---|---|---|---|
| Carbon steel (zinc-plated) | 8,000 PSI (550 bar) | -40C to +150C | General industrial, automotive, construction |
| Stainless steel 316 | 7,500 PSI (517 bar) | -40C to +200C | Food processing, marine, corrosive environments |
| Brass (C360 / CW614N) | 2,000-3,000 PSI (138-207 bar) | -40C to +121C | Marine, low-pressure, corrosion-resistant applications |
Frequently Asked Questions
What size is a standard grease Zerk fitting?
In North America, the most common size is 1/4″-28 UNF with an 8 mm hex. In European and Asian equipment, M6x1.0 and M10x1.5 are widely used. Pipe-thread ports often use 1/8″-27 NPT or 1/16″-27 NPT.
Are metric and imperial Zerk fittings interchangeable?
No. Metric threads have different pitch and diameter from UNF threads, and NPT threads are tapered. Installing the wrong thread will damage the port. Always match the original thread specification or retap the port.
What is the torque for installing a Zerk fitting?
As a general guideline for steel fittings into steel ports: 1/16″ NPT typically 10-15 ft-lb (13.5-20.3 Nm), 1/8″ NPT approximately 15-20 ft-lb (20-27 Nm). For metric fittings, hand-tight plus 1/4 to 1/2 turn is usually sufficient. Over-tightening can split the port or distort the check valve. Always follow the equipment manufacturer’s specification when available.
When should I choose stainless steel over zinc-plated steel?
Use stainless steel 316 in food processing, marine, chemical, or high-temperature environments where zinc plating would corrode or contaminate the process. Carbon steel is the cost-effective choice for dry, indoor industrial use.
Can I use a standard grease gun on angled Zerk fittings?
Yes. A flexible hose and a locking coupler with adequate jaw clearance can engage 45 and 90 degree fittings. For deeply recessed angles, use an angled adapter or extension nipple to improve access.
Shop Grease Zerks and Fitting Kits
Browse the grease fittings category, grease nipples category, and Zerk fitting kits for individual sizes and assortments. Popular items include the 1/16″ NPT Zerk, M12x1.25 metric Zerk, and protective caps.
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Related: Some machines take oil, not grease, through their zerks — see our guide to choosing an oil gun for zerk fittings.
