Brass Grease Nipples | M6 to M12 and BSP Zerk Fittings

Overview

Brass grease nipples, also called brass Zerk fittings, are threaded check valves that screw into a bearing housing or lubrication port so grease reaches the spot that needs it. A spring-loaded hardened steel ball opens under coupler pressure and reseals when the coupler is removed, keeping dirt and washdown water out.

This page covers the brass material line only: M6 to M12 metric threads and 1/8 in to 1/4 in BSP. Steel nipples, grease gun selection, and relocation fittings have their own pages, linked below. Typical placements: vehicle chassis points, conveyor and mixer bearings, deck hardware, agricultural machinery.

Specifications

The tables collect the declared ratings; burst-pressure and corrosion-hour figures are not published.

Body Styles, Threads, and Finish

Five body styles are offered. Straight (0-degree) fittings suit open, accessible points. The 45-degree and 90-degree bodies route grease around obstructions so the coupler sits squarely on the ball. Button head fittings sit low behind protective covers, and flush fittings present a smooth face that resists snagging. The grease fitting types guide explains when to pick each.

Metric threads follow the ISO metric 6g class, imperial threads 2A. A loose thread weeps grease; an oversized thread can crack a cast boss. DIN 71412 and BS 1486 dimensions make them interchangeable with other fittings built to the same standards.

The body is brass, which machines cleanly and resists rust staining. Electroless nickel plating suits fittings facing salt air, chemical splash, or frequent washdown; it adds cost, so plain brass is the better value on dry indoor machines. Dimensional drawings are available on request.

Installation

Clean the tapped hole and threads, then apply PTFE tape or a grease-rated thread sealant. Torque to 20-34 Nm (15-25 ft-lbs) by size: lower half of the range for M6 and M8, upper half for M12 and 1/4 in BSP. Engage at least 6 full threads; fewer threads concentrate load.

Brass has a lower torque ceiling than steel, so use a calibrated wrench, and verify no grease weeps past the threads at working pressure.

Allow 15 mm of radial clearance so a standard 4.5 mm coupler locks on squarely. Where guards leave less room, fit a 90-degree body or relocate the nipple with an extension fitting rather than forcing the coupler at an angle; see the extension fittings page.

For standard sizes, nickel-plated variants, or mixed-thread orders, request a quote with your thread list.

Frequently Asked Questions

Should I choose brass or steel grease nipples?

Brass resists corrosion unplated and suits outdoor, washdown, and salt-air settings without staining paint. Steel takes higher torque but rusts unplated. Near 350 bar continuous, pick steel; brass covers 0-300 bar.

Will these nipples fit my existing grease gun?

Yes. The head is the standard 4.5 mm ball defined by DIN 71412, so push-on and locking couplers seat correctly. For high-pressure work, a four-jaw locking coupler grips better; see our 4-jaw high pressure coupler page.

What do the thread codes mean?

M6x1.0 means 6 mm diameter with 1.0 mm between crests. M8 and M10 each come in two pitches, so gauge before ordering. BSP threads are sized by pipe bore, not outside diameter.

When should I pay for nickel plating?

Choose electroless nickel when the fitting faces salt air, corrosive washdown, or chemical splash; it slows attack on the brass. On dry indoor machines, plain brass resists rust staining and costs less.

Should I pick the NBR or the FKM seal?

NBR, the standard seal, handles petroleum greases from -40 °C to +100 °C. FKM (Viton) covers synthetics from -20 °C to +200 °C and harsh chemistry. Choose FKM for hot or aggressive-chemistry points; NBR covers the rest.

How tight should I torque the fitting?

Follow 20-34 Nm (15-25 ft-lbs) by size: low end for M6 and M8, high end for M12 and 1/4 in BSP. Brass yields at lower torque than steel; over-tightening can crack the hex or distort the seat.

Why does grease leak past the ball head?

Leaks past the ball mean the coupler sat at an angle, the system ran above 0-300 bar continuous, or the seal aged. Continuous running above 300 bar shortens seal life; 350 bar is the maximum rating. Replace a weeping fitting; seat the coupler squarely.

Button head, flush, or standard head?

A standard head gives the coupler the most grip. Button head fittings sit recessed behind protective covers. Flush fittings present a flat face for washdown zones. All three share the same valve and ratings; only the shape differs.

Can I plumb these nipples into a centralized lubrication line?

The nipple is the service port, not the distribution network. Centralized systems meter grease through tubing and manifolds; the nipple is the refill interface. If structure buries the point, relocate it with an extension fitting instead of bending hard lines.

Who makes these fittings and how do I order?

These fittings come from a team with deep roots: IsoHiTech Lubrication Systems was founded in 2023, engineering since 2006. To order, email inquiry@isohitech.com or use the quote request page.