DIN 3405 concave flush-type grease nipples are the third major head form for lubrication points. A DIN 71412 taper nipple protrudes as a cone, a DIN 3404 button head presents a wide clamping face, and this type sits flat or countersunk with a shallow concave cup. This page covers M6x1 to G1/4 in zinc-plated carbon steel or 1.4404 stainless steel, in straight, 45°, and 90° forms. For protruding taper heads, see our DIN 71412 grease nipples; for button-head work, see the giant button head grease fitting; other forms are compared in our grease fitting types guide.
Size and Thread Options
Six sizes are available, from M6x1 to G1/4 (BSP), in zinc-plated carbon steel or 1.4404 stainless steel.
| Thread | Length (mm) | Protrusion (mm) | Head Dia (mm) |
|---|---|---|---|
| M6x1 | 8 – 10 | 2.0 | 7 – 8 |
| M8x1 | 10 – 12 | 2.5 | 9 – 10 |
| M8x1.25 | 10 – 12 | 2.5 | 9 – 10 |
| M10x1 | 12 – 15 | 3.0 | 11 – 13 |
| G1/8 (BSP) | 12 – 14 | 3.0 | 10 – 11 |
| G1/4 (BSP) | 14 – 16 | 3.5 | 13 – 14 |
Form A, Form B, and Form C
DIN 3405 configures the head by angle, not thread. Form A is straight at 180° for direct access; Form B turns the cup to 45° when the path is blocked; Form C turns it to 90° for perpendicular access, as our 90 degree grease nipple does for taper heads. With-collar versions stop in a countersunk seat; without-collar versions sit flush or recessed. Slot drive takes a screwdriver where a hex cannot reach; square drive takes a wrench.
Why Standard Couplers Do Not Seat
A standard hydraulic coupler jaws onto a protruding cone or clamps a button; on a flush concave seat it has nothing to grip. Fill the cup through a pointed, pin-pointed, or combi nozzle on a push-type gun; an extension tube with pointed tip reaches recessed points. Spring cone adapters suit standard loads; rubber cone tips suit light loads.
Materials and Temperature Range
Carbon steel carries an 8 – 12 micron zinc plating in clear or yellow chromate, passivated. Choose 1.4404 stainless for marine decks, washdown areas, and corrosive atmospheres. Zinc-plated steel covers -40°C to +120°C; stainless covers -60°C to +200°C.
Installation Torque
Install with a calibrated torque wrench: over-torque strips the thread or cracks the body, and under-torque lets vibration loosen the nipple. Clean and deburr the hole, start the nipple by hand for 2 – 3 turns, then torque. Add no sealant or tape to metric threads; fragments can travel into the grease path. PTFE tape on G threads is confirmed when ordering.
| Thread | Torque (Nm) |
|---|---|
| M6x1 | 8 – 12 |
| M8x1 / M8x1.25 | 8 – 12 |
| M10x1 | 25 – 35 |
| G1/8 (BSP) | Confirm when ordering |
| G1/4 (BSP) | Confirm when ordering |
Grease Compatibility
Grease across NLGI 0 – 3 works, with lithium complex, calcium sulfonate, polyurea, or synthetic PAO thickeners and MoS2, PTFE, or graphite up to 5%. Base oil viscosity of 150 – 2,000 cSt at 40°C stays within push-greasing practice. Avoid strong acids (pH below 3), strong bases (pH above 12), ketones, and aromatic solvents.
Maintenance and Replacement Signals
Inspect monthly on critical points and quarterly on general machinery. Wipe the concave cup before every greasing; a flush cup collects grit that would ride into the bearing. Follow the equipment manufacturer’s interval for grease changes. Replace the nipple when the head deforms, threads damage, or grease seeps during injection.
Honest Limitations
- Low-pressure push-greasing only; locking hydraulic couplers do not fit.
- Dust caps made for taper heads do not fit the flush concave seat.
- G-thread torque depends on the mating part; confirm when ordering.
Not sure this form fits your application? Contact our application team for sizing guidance.
Frequently Asked Questions
How is this form different from taper and button heads?
A taper nipple protrudes as a cone; a button head presents a wide clamping face; this type sits flat or countersunk.
Why will my standard grease gun coupler not connect?
Standard couplers grip a protruding cone or clamp a button; a flush cup offers nothing to grip. Use a pointed, pin-pointed, or combi nozzle.
When should I choose a concave flush-type nipple?
Where a protruding head would be struck or has no room: engine bays, suspension and steering, construction and farm machinery, conveyor lines, and marine deck positions.
How do I choose Form A, B, or C?
By approach angle: Form A straight at 180°, Form B at 45° for blocked paths, Form C at 90° for the tightest gaps.
Are both metric and G (BSP) threads available?
Both metric (M6x1 to M10x1) and G (BSP) threads are available; see the table. Torque for G threads is confirmed when ordering.
What installation torque applies?
8 – 12 Nm for M6x1 and M8x1, 25 – 35 Nm for M10x1; use a calibrated torque wrench.
When is 1.4404 stainless the right choice?
Zinc-plated steel suits dry positions; choose 1.4404 stainless for marine decks, washdown areas, and corrosive exposure.
Which greases are compatible?
Standard greases in NLGI 0 – 3 with lithium complex, calcium sulfonate, polyurea, or synthetic PAO thickeners, and MoS2, PTFE, or graphite up to 5%.
How do I maintain these nipples?
Inspect monthly on critical points, quarterly elsewhere. Wipe the cup before greasing so debris cannot ride into the bearing. Change grease on the equipment manufacturer’s interval.
Who is IsoHiTech?
IsoHiTech Lubrication Systems is a lubrication equipment supplier founded in 2023, engineering since 2006. For selection help or a quote, send us a request through our contact page or write to inquiry@isohitech.com.
