A drill point die size chart from L1 to L7 is the one document that decides whether your die order arrives usable. Everything else in a quotation — price, lead time, material, coating — is negotiable later. The row you point at on the chart is not: it fixes the drill diameter, the flute length and the point profile that your pointing machine will press into every blank for the life of the set.
The problem is that most buyers read these charts the way they read a bolt catalogue, top to bottom, looking for a screw size and grabbing the code next to it. That works until the day two suppliers hand you charts with the same die codes and different columns, or the day a die arrives that matches the chart and still produces a screw your customer rejects. This article covers what each column in an L-series drill point die chart actually measures, in what order to read them, which cells are load-bearing and which are informational, and exactly what to ask a supplier for when the chart you have been sent has headings but no numbers.
What an L-series chart is, structurally
ZLD Precision Mold, a Dongguan drill point die maker, publishes its range as a seven-series system running L1 through L7. The claim it makes for that chart is a structural one: every die code maps to a screw size — IFI #4 through #14 in the inch system and DIN ST2.9 through ST6.3 in metric — with drill diameter Dø, point diameter, wire diameter, flute length and die style given per code. A selection chart at that level of completeness is genuinely uncommon in this niche, where a great many suppliers quote from a screw size and a phone call.
Structurally, then, a row in the chart is a complete point specification, and the die code is the shorthand for it. That is the mental model to hold. The code is not a size in itself; it is a pointer to a set of five or six dimensions that together define one drilling point. Two rows can share a screw size and differ in every other column, which is precisely why the chart exists.
A well-formed row answers four separate questions:
- Which screw does this fit? — the screw size columns, in both designation systems.
- What hole will it drill? — drill diameter Dø.
- How much material can it clear before the thread engages? — flute length.
- What shape of point is it? — point diameter and die style.
If a chart you are handed cannot answer all four for a given row, it is not a selection chart, it is a price list.
Column by column: what each field actually measures
This is the dictionary. Read a chart with it beside you and the disagreements between two suppliers' charts stop being mysterious.
| Column | What it measures | Where it is measured | What it decides |
|---|---|---|---|
| Die code (L1–L7 plus sub-code) | Index into the supplier's own cavity library | Not a dimension | The exact cavity you are ordering; the only field the supplier will manufacture from |
| Screw size (IFI) | Inch-system nominal screw designation, #4 to #14 | Nominal designation, not a measured value | Which finished screw family the point belongs to |
| Screw size (DIN) | Metric self-drilling screw designation, ST2.9 to ST6.3 | Nominal designation | The metric equivalent of the same row — check it is an equivalence, not a separate offering |
| Drill diameter (Dø) | Diameter across the widest part of the drilling point | On the formed point, at the cutting lips | Hole size produced, and therefore thread engagement in the base material |
| Point diameter | Diameter at the defined point section, before the drill flat | On the formed point, at the section the supplier's drawing calls out | Point stiffness and entry behaviour; also how the point relates to the shank |
| Wire diameter | Shank diameter of the blank the die is designed to receive | On the incoming blank, before pointing | Whether the die will accept your header's output at all |
| Flute length | Axial length of the flute from tip toward shank | On the formed point | Maximum material thickness the point can drill before the thread starts to bite |
| Die style (MA / MB / MC) | Cavity family designation | Not a dimension | Point profile, flute form and relief — a different point for the same nominal size |
| Material / coating (where shown) | Substrate grade and optional surface treatment | Property of the die, not the screw | Die life and tolerance to your machine's condition |
Three of those columns are worth extra attention because they are where mis-orders concentrate.
Wire diameter is the compatibility gate, not the screw size. The die receives a blank from your header, and if the wire diameter on the row does not match what your header actually produces, nothing else on the row matters. Blank diameter drifts with wire lot and header die wear; measure yours before you order rather than reading it off the screw print. This is the single most common cause of a die that "does not fit" on arrival.
Flute length is a drilling-capacity field disguised as a dimension. The flute has to hold and clear displaced material until the point breaks through the base metal. If the thread reaches the workpiece before the point breaks through, the screw stops drilling and starts jacking — the failure your customers report as "it stalls in 4 mm steel." The relationship between flute length and drillable thickness is not linear and is not the same across die styles, so treat the flute length column as an input to a drilling test rather than a specification you can convert to millimetres of steel on paper.
Drill diameter Dø is measured on the point, not on the finished screw. It is a formed dimension on a soft blank, before heat treatment and before plating. If your incoming inspection measures plated screws against the chart's Dø, the numbers will disagree and the die is not at fault. Get the measurement condition written on the drawing.
How to read the chart in the right order
Working from screw size downward is the natural instinct and the wrong sequence. It leaves the two most restrictive fields until last, after you have already picked a code.
Read it in this order instead:
- Wire diameter first. Filter to the rows your header can feed. This eliminates most of the chart immediately and eliminates it for a physical reason.
- Screw size second, in whichever designation system your customer's drawing uses. Note the equivalent in the other system and carry both on the order.
- Drill diameter Dø third. Check it against the hole size your application needs in the base material, and against whatever your incumbent point produces if you are switching.
- Flute length fourth, against the maximum base-material thickness you have to drill in production — not the nominal thickness on the drawing, the worst case you actually see.
- Die style last, and never by default. If the chart offers MA, MB and MC against your row, that is a real choice with a real effect on the point, and it deserves its own conversation with the supplier.
- Material and coating after the geometry is settled. Substrate and surface treatment change die life, not the screw the die produces.
Two questions to settle before you use any L-series chart, because the answers are supplier-specific and not visible on the page:
- Which direction does the series run? Whether L1 is the smallest code or the biggest is a convention, not a standard. It is not stated in the material available for ZLD's chart, and it will not be stated on most competitors' charts either. Ask, and ask in writing — a mis-read series direction turns a whole order into scrap.
- Does one code equal one screw size, or a band? Some series systems assign a code per discrete size; others assign a code to a size range and vary sub-codes within it. This changes how many sets you carry to cover your product range, which is a real inventory number.
The chart you should ask for
Here is the practical part. The column structure above is documented; the numbers behind it are not published in any form you should be quoting from. Do not fill them in from a competitor's catalogue, do not infer them from screw dimensions, and do not let a salesperson give them to you verbally. Send this template and ask for it back completed and stamped.
| Die code | Screw size (IFI) | Screw size (DIN) | Drill dia. Dø | Point dia. | Wire dia. | Flute length | Die style | Substrate | Coating |
|---|---|---|---|---|---|---|---|---|---|
| L1 | — | — | — | — | — | — | — | — | — |
| L2 | — | — | — | — | — | — | — | — | — |
| L3 | — | — | — | — | — | — | — | — | — |
| L4 | — | — | — | — | — | — | — | — | — |
| L5 | — | — | — | — | — | — | — | — | — |
| L6 | — | — | — | — | — | — | — | — | — |
| L7 | — | — | — | — | — | — | — | — | — |
Attach four instructions to it:
- State the unit and the tolerance on every dimensional column. A number without a tolerance band is not a specification. Ask specifically whether the tolerance is symmetric or one-sided, because on drill diameter that difference is functional.
- State the measurement condition. As-formed blank, post-heat-treatment, or finished plated screw. One line on the chart, and it prevents a year of arguments with incoming inspection.
- State whether the IFI and DIN columns are equivalences or alternatives. If ST4.2 and #8 sit on the same row, confirm that one die code serves both, rather than the chart listing two families that happen to share a line.
- Ask for one dimensioned cavity drawing for the row you intend to buy first. The chart tells you what the point should be; the drawing tells you what the die is.
A supplier who returns that table fully populated, with tolerances and a measurement condition, has told you more about their engineering discipline than any factory tour would. A supplier who returns it with three columns filled and an invitation to send a screw sample instead has also told you something.
Common questions
Is the L1–L7 system an industry standard?
No. It is a supplier's own series designation. Self-drilling screws themselves are standardised — SAE J78 and IFI 113 on the inch side, DIN 7504 and the ISO 15480 family on the metric side — but the die codes that produce them are house systems, and one maker's L4 is not portable to another maker's L4. That is exactly why the die code on your purchase order has to travel with the full dimension set behind it, and why a repeat order placed on a code alone, to a new supplier, is a gamble.
Can I order from a screw sample instead of the chart?
Yes, and for non-catalogue point designs it is often the better route. ZLD takes two RFQ entry points: a drawing, or photographs of the screw or of the old die. Sending a physical sample of the screw you want to reproduce — and, if you have one, the worn die that used to make it — removes an entire class of translation error. Ask for the resulting die to be documented back to you as a completed chart row, so that the reorder in eighteen months does not depend on someone finding the same sample.
Why do two suppliers quote different prices for the same die code?
Because the code is not a common language, and because the substrate, the cavity finish, the tolerance band and the amount of engineering review folded into the quote vary widely. Price differences in Chinese tooling quotations usually decode to specification differences rather than margin differences — the same pattern covered in why quotes for the same spec differ. Normalise the specification first, then compare.
How many sets do I actually need to cover my range?
Count distinct rows, not distinct screw sizes. If your product range spans several screw sizes and more than one point style, the row count is the tooling inventory you are committing to. Do that arithmetic before you negotiate unit price, because the number of sets, not the price per set, is what determines your tooling spend.
What to ask the supplier next
- Send the blank L1–L7 template above and ask for it returned complete, with units, tolerances and measurement condition stated.
- Ask which direction the series runs and whether each code covers one size or a band.
- Ask for the IFI-to-DIN equivalence to be confirmed in writing per row, not inferred.
- Ask for one dimensioned cavity drawing for the first row you intend to buy.
- Send a screw sample and, if available, an old die, and ask for the resulting build to be documented back as a chart row you can reorder from.
- Ask for a trial set before committing to a program, and run it on your own machine against your incumbent dies.
- Ask what happens on a reorder — whether the cavity data is archived under your part number, and how long the supplier keeps it.
Applying that to a real supplier is the point of the exercise. ZLD Precision Mold publishes the L1–L7 structure and the column set, accepts trial orders from a single set, and quotes standard samples in 3–4 days with production lead time around 10 working days on the company's own stated terms; the factory profile is the place to check the registry-level facts before you send a specification. The same evaluation habits apply to any narrow-specialist tooling supplier — the broader version is covered in the China hardware manufacturer guide. Get the chart populated first. Everything downstream is easier once the rows have numbers in them.