Grade BLU Threading Inserts
If you've spent any time threading stainless steel, titanium or Inconel, you'll know that not all inserts are created equal. The wrong grade burns through cutting edges fast, leaves messy threads and turns a five-minute job into a tooling-cost nightmare.
This guide walks through what Carmex's Grade BLU actually is, the materials it's designed for, the thread profiles it's available in, and how to know whether it's the right grade for your next job.
What is Grade BLU?
Grade BLU is Carmex's premium PVD triple-layer coated sub-micron carbide grade. Don't let the spec sheet jargon throw you — here's what each part of that actually means on the shop floor:
- Sub-micron carbide: The base substrate is made from extremely fine carbide grains, giving the insert its toughness and edge strength.
- PVD coating: Physical Vapour Deposition lays down a super-hard coating at lower temperatures than CVD — it preserves the sharp cutting edge that threading demands.
- Triple-layer: Three coating layers stacked together — each tuned for a different job (heat resistance, wear resistance, chip-flow). Together they last significantly longer than single-layer coatings under demanding conditions.
In real terms? Sharper edges, longer life, better surface finish, and far fewer insert changes per shift.
The Materials Grade BLU is Built For
This is where Grade BLU earns its keep. The coating chemistry has been optimised specifically for the materials that wear ordinary inserts down fastest.
In ISO classification terms, Grade BLU covers M10–M20 (stainless), K05–K20 (cast iron), N10–N20 (non-ferrous metals) and S10–S20 (titanium and high-temperature alloys). It's the closest thing in our catalogue to a true all-rounder — provided you're not threading carbon steel.
Heads up: For carbon and low-alloy steels, our standard recommendation is Grade BMA instead. BMA is optimised for P-class materials (P10–P30) and gives better tool life on those workpieces than BLU does.
Why Engineers Reach for BLU on Stainless
Stainless steel is a notorious insert-killer. It work-hardens fast, conducts heat poorly (so the cutting edge takes the heat hit), and produces stringy, gummy chips. Three things that destroy uncoated or poorly-matched carbide inserts in minutes.
Grade BLU's PVD coating handles all three:
- Heat resistance: The coating's outermost layer reflects cutting heat back into the chip rather than the edge.
- Edge sharpness: PVD doesn't round the cutting edge the way thicker CVD coatings can — so the insert cuts cleanly without smearing or rubbing.
- Chip control: The combination of edge geometry and low coefficient of friction breaks chips properly instead of letting them string out.
The end result is consistent threads, longer tool life and predictable cycle times — which is what you actually care about when you're costing jobs.
Pick the Right Thread Profile
Grade BLU is available across the full Carmex 16ER laydown range. Here's how to pick the right profile for your job:
A quick rule of thumb: if you're producing parts to UK or European drawings, you'll mostly want ISO Metric. For US-spec or aerospace work, UN or UNJ. For pipework and sealing, NPT (American) or BSPT (British). Whitworth still has a strong presence on older British machinery, plumbing and gas fittings.
Full-Profile vs Partial-Profile — Which to Choose?
Every thread profile in 16ER comes in two flavours: full-profile and partial-profile. The trade-off is simple:
All BLU inserts in our current pack-of-2 promotion are full-profile — built for fast, accurate, repeat-ready threading.
How to Get Maximum Tool Life from Grade BLU
Even the best insert won't perform if the holder, speeds and feeds are wrong. A few quick principles:
- Match the holder: Use a Carmex 16ER holder where possible. Cross-brand mixing (Seco/Sandvik holders with Carmex inserts) can compromise pocket geometry and reduce tool life — even though the inserts are nominally interchangeable.
- Anvil tilt for steep helix angles: If you're threading fine pitches on small diameters, swap to the correct interchangeable anvil to match the helix.
- Cutting speeds for stainless: Start around 80–120 m/min for 304/316 stainless. Drop to 60–90 m/min for 17-4 PH or duplex stainless. Always run flood coolant on stainless threading.
- Number of passes: For thread depths over 1.5mm pitch, use radial infeed and 8–14 passes rather than fewer heavy ones — it saves the cutting edge.
The May Promotion: Try BLU in a Pack of 2
Threading inserts are usually only sold in packs of 10, which makes trying a new grade an expensive commitment. For one month only, we're running our 2-pack trial offer on the most popular 16ER Grade BLU profiles — just £9.99 per pack of 2 (£4.99 each).
Available across the full range — ISO Metric (M5 to M48), UN, UNJ, NPT and Whitworth profiles. Whether you want to test BLU on a difficult stainless job or just keep a couple in the drawer for next time, the pack-of-2 takes the cost-of-trying out of the equation.
Got a Tricky Threading Job?
If you're not sure which grade or profile is right for your application, our technical team are here Monday to Friday, 8:30am to 5pm. Whether it's a one-off prototype or a production run, we'll help you spec the right insert first time.
Call us on 01732 887334 or email info@protool-ltd.co.uk — we'd rather take ten minutes to recommend the right tool than have you burn through a pack on the wrong one.
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