If you run a screw header machine on stainless steel wire — 304, 410, 416 or similar grades — you already know the pattern: the die set holds up, but the ejector pins start galling, scoring, and losing surface finish within a few shifts. Every pin change means stopping the header, re-tempering adjustments, and scrap parts.
Stainless work-hardens fast. The blank grips the die cavity harder, extrusion loads spike, and the ejector pin takes repeated high-pressure sliding contact at elevated temperature. A standard alloy tool steel pin simply was not designed for this duty cycle.
That is where M42 cobalt high-speed steel earns its place.
What M42 brings to an ejector pin
M42 (AISI M42 / DIN 1.3247 / JIS SKH59) is an 8% cobalt high-speed steel. The cobalt addition changes two things that matter for KO pins:
- Hot hardness. M42 retains hardness at temperatures where ordinary HSS softens — critical when the pin sees thousands of ejection cycles per hour against a hot blank.
- Higher attainable hardness. Vacuum heat treated and triple tempered, M42 reaches HRC 65–68, giving superior resistance to abrasive wear and galling against stainless.
Combined with a precision ground and polished surface, the result is an ejector pin that keeps a clean, consistent ejection stroke long after a standard pin would need replacement.
M42 vs H9 vs D2: a quick selection guide
Buyers often ask which grade is "best." The honest answer: it depends on the wire and the volume.
| Grade | Typical hardness | Best suited for | Notes |
|---|---|---|---|
| D2 | HRC 60–62 | Carbon steel screws, short runs, low load | Economical, good general wear resistance |
| H9 | HRC 61–63 | General screw header work, carbon & low-alloy wire | Balanced toughness and wear resistance |
| M42 | HRC 65–68 | Stainless steel wire, long runs, high loads | Cobalt HSS, outstanding hot hardness |
| Carbide (WC) | HRA 88–92 | Extreme volume, non-ferrous, thin pins | Highest wear life, more brittle, higher cost |
A practical rule of thumb: if you are producing stainless steel screws, or your ejector pins are wearing out faster than your die inserts, moving the pin material up to M42 usually pays back quickly in reduced downtime.
Specifications available from JingHong Pins
- Material grade: M42 (8% cobalt HSS), vacuum heat treated
- Hardness: HRC 65–68
- Standard diameter range: φ0.8 mm – φ40 mm
- Non-standard sizes: made to print, tolerances down to ±0.01 mm
- Common lengths: 40 mm, 150 mm, custom lengths on request
- Surface: precision ground, polished
- Application: screw header machines, cold heading dies, stainless screw tooling
We also supply matching first punch / second punch sets and die inserts in H9, M2, M42 and tungsten carbide, so the whole die set can be specified with consistent material logic instead of mixed guesses.
Who buys M42 ejector pins
- Producers of self-tapping screws in 410/430 stainless
- Drywall screw lines running long campaigns
- Automotive fastener suppliers where line-down cost is high
- Header machine rebuilders replacing full die sets
- OEM fastener projects requiring made-to-print KO pins
If your current pins show galling, pick-up, or dimensional loss on the working face within the first month, that is the market-typical signal to move to a cobalt HSS grade.
Why source from JingHong Pins
Located in Dalang, Dongguan — one of China's densest fastener and mold manufacturing clusters — JingHong Pins is a factory-direct producer of precision fastener tooling with 26 years of experience. We do cold heading dies, punches, and ejector pins — and only fastener tooling.
In-house CNC grinding, cylindrical finishing, EDM and wire-cut, vacuum heat treatment with material certificates, full dimensional inspection before packing. OEM / ODM, made to your drawing or sample, English communication from quote to delivery, replies within 24 hours on weekdays.
Send us your pin drawing
If you are running stainless steel screws and burning through ejector pins, send us the pin specifications or a photo of the failed pin — we will recommend the right grade (M42, M2, or carbide) and quote within 24 hours on weekdays.