What is the difference between the L7 and L6 series?

Flute length. L6 covers 15.8–17.0ℓ and L7 covers 17.8–19.0ℓ. Both are offered in MC (Style III) only and span the same drill diameter range (4.3–5.7 mm). The only reason to specify L7 over L6 is insufficient penetration depth — there is no other performance difference between them.

When do I actually need L7?

When the screw must penetrate steel thicker than about 12 mm, or when stacked layers add up beyond what L6 can reach. In practice this concentrates in heavy structural steel, thick base plates and multi-layer structural connections. If your actual thickness falls inside L6's range, L6 is usually the more economical choice.

Can L7 dies be made in high-speed steel?

Carbide is generally recommended at this thickness. Cutting time is long and heat load is high, and HSS life under these conditions is typically much shorter. For small trial runs or specification validation you can discuss an HSS option with your supplier, but set expectations on replacement frequency accordingly.

What die codes are available in L7?

Codes are named by drill diameter, running from L7-43 to L7-57 for drill diameters of 4.3 mm to 5.7 mm. Confirm specific availability against the specification table, or send us your screw specification and we will narrow the candidates.

L7 Series Drill Point Dies: The Longest Flute, for Extra-Thick Structural Steel

L7 is the longest-flute series in the drill point die range. It exists for one reason: when L6's flute length cannot penetrate the target thickness, L7 is the next step up.

This guide covers L7's actual parameters, how it really differs from L6, and when you probably do not need it.

Specification overview

Parameter	L7 series
Flute length (ℓ)	17.8 – 19.0 mm (nominal 19.0)
Die style	MC (Style III) only
Drill diameter	4.3 mm – 5.7 mm
IFI sizes	#12 – #14
DIN sizes	ST5.5, ST6.3
Die code range	L7-43 to L7-57
Recommended die material	Tungsten carbide
Target substrate	Steel above 12 mm, or stacked layers reaching that thickness
Governing standards	IFI 113, DIN 7504

Flute length, style and drill diameter are specification-table values. Material recommendation and target substrate are practical guidance by application; actual selection should be confirmed against your production conditions.

How L7 really differs from L6

One thing to be clear about up front: L7 differs from L6 in flute length, not in grade.

	L6	L7
Flute length ℓ	15.8 – 17.0 mm	17.8 – 19.0 mm
Die style	MC only	MC only
Drill diameter	4.3 – 5.7 mm	4.3 – 5.7 mm
IFI sizes	#12 – #14	#12 – #14

The two cover identical screw sizes and drill diameters in the same style. The only variable is roughly 2 mm of additional flute length.

Which means: if your thickness sits within L6's range, switching to L7 buys you nothing. It lengthens the drilling stroke, adds assembly time and consumes more wire. L7 is for cases where penetration depth falls short — it is not a better L6.

When L7 is genuinely required

Three typical scenarios:

Single-layer extra-thick plate — target substrate above 12 mm in solid steel. Common in heavy structural steel main framing and thick base plates.

Stacked layers — no single layer is thick, but the stack exceeds L6's reach. Multi-layer structural connections are especially prone to this: the specification gets sized against a single layer, and the shortfall only shows up in production. Size against the total thickness the screw actually passes through, not the individual layer.

Replacing bolted connections — steel-to-steel joints where pre-drilling is impractical or too costly, using self-drilling screws in place of through-bolts. Flute length requirements in these applications are frequently underestimated.

Why carbide is recommended at this thickness

L7 applications stack several pressures on the die:

Extended cutting time. The longer the flute and the thicker the plate, the longer the drilling phase lasts. Light-gauge self-drilling screws finish drilling almost instantly; a screw penetrating a thick multi-layer connection can spend several seconds in active cutting. Throughout that period the point has to hold its cutting geometry while temperature climbs.

High material removal. Penetrating thick plate generates far more chip volume to form, convey and evacuate than sheet applications. That tests both the flute geometry and the dimensional stability of the die cavity.

High heat load. Extended cutting means point temperatures run considerably higher than in sheet applications. Actual temperatures depend on drilling speed, substrate and cooling conditions, but the thermal cycling in this regime places higher demands on die material heat resistance.

With these stacked, HSS life is typically much shorter. This does not mean HSS is unusable — it remains worth considering for small trial runs or specification validation, provided expectations on replacement frequency are set accordingly. For high-volume, stable L7 production, carbide is the more common choice.

Carbide die life under normal operating conditions runs around two million pieces, with actual figures varying considerably by screw material, machine condition and operating discipline. See tungsten carbide vs HSS drill point dies for the full material comparison.

Drill Point Die Selector

Enter screw size and plate thickness to get the matching die code

Open the selector tool

Practical notes for running L7

Wire is a precondition. A longer flute needs more material during forming, raising the demands on wire diameter and ductility. Wire that runs hard or lacks ductility carries a more visible cracking risk on long-flute specifications. See our fastener wire mechanical properties reference.

Confirm the die pocket. L7 is MC (Style III) only, with a correspondingly large die body. Verify your header can accommodate it — this is a common sticking point in L7 inquiries.

Preforming matters more. Long flutes are more sensitive to blank consistency. Deviations at the preform stage get amplified in final forming, showing up as uneven flute length or an off-center point.

Run a trial before committing. L7 conditions are more demanding than standard specifications, and real drilling performance depends heavily on substrate, machine and operator. Validating on your actual substrate beats extrapolating from a parameter table.

First confirm L7 is what you need

Two misjudgements come up repeatedly:

Underestimating total thickness — sizing L5 or L6 against a single layer, then failing to drill through the actual stack. Size against the total thickness the screw passes through.

Over-specifying — thickness actually sits within L6's range, but L7 gets chosen "to be safe." The result is longer spin-down at assembly and higher wire consumption, raising cost rather than lowering risk.

If you are unsure which tier applies, enter your thickness and screw specification into the drill point die selector for candidate series and codes. For the full decision sequence, see the drill point die selection guide.

Summary

L7 is the longest-flute tier in the range (17.8–19.0ℓ), MC style only, covering IFI #12–#14 / DIN ST5.5–ST6.3, with codes from L7-43 to L7-57. It solves exactly one problem: insufficient penetration depth.

The test for specifying it is a single question — does the total thickness the screw must pass through exceed what L6 can reach? Below that, L6 is usually the more economical choice.

Zhonglianda Precision Mold produces the full L1–L7 range, with L7 primarily in tungsten carbide. Standard samples typically take 3–4 working days, and we accept trial orders of a single die. View the full specification table or send your screw specification.