One Item Instead of Three: The Screw, the Washer and the Coating
A distributor that sells a DIN 912 M3 × 8 A2 screw, a DIN 9021 washer and a tube of threadlocker sells three items, and the fitter assembles them. Built as one set, the washer sits under the head and a dry coating sits on the thread, so the fitter takes one part from one bag and drives it. EKINSUN LTD builds these sets to the distributor’s or the OEM’s specification, from a sample lot to runs of 50,000 sets.
The drawing shows what such a specification fixes: every head dimension inside the ISO 4762 limits for M3 (the knurled head may be up to 5.68 mm across, the plain head up to 5.5 mm), the length tolerance of 7.71 to 8.29 mm for an 8 mm screw, and the washer drawn by its outside diameter and thickness. A knurled head and a plain head are both DIN 912; if a sample and the standard differ, say which one rules before the run, because a coated screw cannot be reworked.
ISO 4762 Head Sizes M3 to M8 — What the Washer Has to Cover
A DIN 912 M3 head is 5.5 mm across and 3 mm high with a 2.5 mm socket at least 1.3 mm deep, and the screw is threaded to the head up to 20 mm long, so an M3 × 8 has no plain shank. The head diameter decides how much the washer adds: on M3 a DIN 433 washer is only 0.5 mm wider than the head, a DIN 9021 washer 3.5 mm wider.
| Size | Pitch P | Head Ø dk max | Knurled head Ø dk max | Head height k max | Socket s | Socket depth t min | Threaded to the head up to length |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.5 | 5.68 | 3 | 2.5 | 1.3 | 20 |
| M4 | 0.7 | 7 | 7.22 | 4 | 3 | 2 | 25 |
| M5 | 0.8 | 8.5 | 8.72 | 5 | 4 | 2.5 | 25 |
| M6 | 1 | 10 | 10.22 | 6 | 5 | 3 | 30 |
| M8 | 1.25 | 13 | 13.27 | 8 | 6 | 4 | 35 |
Values per ISO 4762:2004 Table 1. The full table M3–M36 with thread lengths is on socket head cap screws.
DIN 125, DIN 9021 or DIN 433 — Which Washer Goes Under the Head
All three washers for M3 have a 3.2 mm hole; the outside diameter and the thickness are what change. DIN 9021 3.2 × 9 × 0.8 mm has a bearing area of about 56 mm² against 30 mm² for DIN 125-A 3.2 × 7 × 0.5 mm, 1.8 times as much, which is why it is chosen for slotted and oversized holes, plastic housings and thin sheet. DIN 433 (3.2 × 6 × 0.5 mm) is the small washer for tight spaces next to a wall or a second screw.
| Size | Screw head Ø | DIN 433 / ISO 7092 (small) | DIN 125-A / ISO 7089 (normal) | DIN 9021 / ISO 7093-1 (large) |
|---|---|---|---|---|
| M3 | 5.5 | 3.2 × 6 × 0.5 | 3.2 × 7 × 0.5 | 3.2 × 9 × 0.8 |
| M4 | 7 | 4.3 × 8 × 0.5 | 4.3 × 9 × 0.8 | 4.3 × 12 × 1 |
| M5 | 8.5 | 5.3 × 9 × 1 | 5.3 × 10 × 1 | 5.3 × 15 × 1.2 |
| M6 | 10 | 6.4 × 11 × 1.6 | 6.4 × 12 × 1.6 | 6.4 × 18 × 1.6 |
| M8 | 13 | 8.4 × 15 × 1.6 | 8.4 × 16 × 1.6 | 8.4 × 24 × 2 |
Price for one size: tap its row above, or send the screw and washer. A2, A4 or steel; any washer standard or a drawing; from 1 piece.
Nominal sizes per ISO 7092, ISO 7089 and ISO 7093-1. Washers outside these series, in other thicknesses or materials, are on custom washers and washer types.
Captive or Loose: Why a 3.2 mm Washer Falls Off an M3 Screw
A DIN 9021 or DIN 125 washer for M3 has a 3.2 mm hole and the thread is 3 mm across, so a washer slid onto a finished screw drops off the end. A captive washer needs a hole smaller than the thread’s outside diameter, placed on the blank before the thread is rolled: that is the SEMS method, with washer holes made for it. With the standard washer the set is delivered as screw and washer packed together, or the coating zone and a light press fit are agreed on the drawing. Say which one the fitter expects; it changes the washer, not only the price.
The SEMS forms, their washer pairings and sizes are on SEMS screws.
Microencapsulated, Nylon Patch or Liquid — Choosing the Coating
On an M3 A2 screw a pre-applied coating replaces the medium-strength liquid threadlocker that a buyer who writes “Loctite or a technically equivalent alternative” usually means. A pre-applied coating replaces that step; the choice is between a microencapsulated adhesive that locks and seals, and a nylon patch that holds by friction and can be refitted.
| Microencapsulated adhesive (DIN 267-27) | Polyamide / nylon patch (DIN 267-28) | Liquid threadlocker at assembly | |
|---|---|---|---|
| How it holds | Capsules break on tightening, the adhesive cures in the thread and also seals it | A plastic patch wedges the thread; holds by friction, a retainer rather than a lock | Adhesive applied by the fitter, cures in the joint |
| Sizes in the standard | M3 to M39 coarse; steel and stainless | M3 to M18 coarse | — |
| Temperature | −50 to 100 °C in the standard, up to 150 °C by application; precote 80: −60 to +170 °C | −50 to +120 °C, up to 150 or 200 °C by application | per product |
| Reuse | One assembly; refit with a new screw or liquid | Several refits with falling torque | Clean and re-apply |
| Cure | precote 80 / 80-8: DIN 267-27 values after 6 h at room temperature, full strength after about one day | None — works as soon as it is in | per product |
| On the assembly line | Nothing to dose; screw goes straight in | Nothing to dose | A dosing step per screw, and a check that it was done |
| Choose it when | The joint must not loosen and may need sealing | The screw is taken out and refitted in service | Quantities are small or the line already doses |
Three points matter on an M3 A2 screw. The coating needs its small-thread version: precote 80-8 is made for threads up to M6 or pitches up to 1 mm, and Henkel lists its P3 microcapsules as not suited to fasteners of M6 or smaller. Stainless needs a coating made for it: Henkel names DRI 204 and DRI 2045 as designed for plated and stainless fasteners. And colour does not show strength: the precote 80 datasheet lists red and states that colour is not a primary product feature, so a blue, yellow or red coating is specified by product or torque, never by colour alone.
Where the Coating Sits and How the Torque Is Checked
The coating zone is given as a start from the thread end and a length, and on a short screw it is a design decision: an M3 × 8 has 16 threads of 0.5 mm, the first one or two left clean so the screw starts by hand, and the coating must stop short of the washer so the washer still seats flat. The zone should cover the threads that engage in the tapped hole or the nut. Datasheet torques are measured on M10 screws, so for M3 the breakaway torque is measured on the sample lot in your mating thread, and the same check is repeated on each production lot.
A 50,000-Set Run: Sample Lot, Approval, Build, Packing
A run of 50,000 sets is built in five steps: confirm the head form, the washer standard, the coating product and zone on an approval drawing; build a sample lot and measure the breakaway torque; build the run from the approved sample; pack and label; ship with the papers. Coated parts keep: precote gives 4 years at up to 30 °C and 65 % relative humidity, so a yearly quantity can be built once and called off in parts.
| Item | What you specify | How we build it |
|---|---|---|
| Screw | Standard (DIN 912 / ISO 4762, ISO 7380, ISO 14580), size, length, A2 (1.4301 / 304), A4 (1.4404 / 316L) or property class; plain or knurled head | Standard screws for the set, or made to drawing from 1 piece |
| Washer | DIN 433, DIN 125, DIN 9021 or d1 × d2 × h; A2 or A4; captive or packed loose | Placed under the head before coating, so the coating never reaches it |
| Coating | Microencapsulated or nylon patch; product or breakaway torque; zone; colour | Applied to the stated threads; breakaway torque checked per lot |
| Run | Sets per call-off and per year | Sample lot first, then the run; the more sets per lot, the lower the unit price |
| Packing | Bags of 100, 500 or 1,000, cartons, labels | Neutral packaging, your part number on the label, delivery to your customer if you wish |
| Papers | Material certificate, coating and torque record, dimensional report | EN 10204 3.1 for the screw material; inspection report with each lot |
A set to your specification? Name the screw, the washer, the coating and the quantity per call-off. Standard sizes can also be supplied from stock; sets with washer and coating are built from a sample lot up to tens of thousands of sets, and the more sets per lot, the lower the unit price. Quote in 12 hours.
For Distributors: Neutral Packaging, Your Part Number, Delivery to Your Customer
A distributor’s set ships in bags of 100, 500 or 1,000 without the EKINSUN name; most enquiries for coated screw sets come from industrial distributors who supply a maintenance department or a production line. Each bag carries the distributor’s own part number and quantity on its label and ships either to the distributor or straight to the end customer’s goods-in. Sizes and sets no catalogue lists are made from 1 piece, so the same supplier covers the odd size and the run.
Catalogue or Built to Order
Common coated DIN 912 sizes in quantities of a few hundred pieces are a catalogue item and the cheaper choice. A set with a washer, a stated coating zone, a small stainless size or your own label is where the catalogue stops.
| What you need | In the catalogue? | What we do |
|---|---|---|
| Common DIN 912 sizes with a factory microencapsulated coating, a few hundred pieces | Yes — industrial distributors list them | Buy it there, or ask us: standard sizes can also be supplied from stock, and the more pieces, the lower the unit price. |
| Screw, washer and coating as one item with one part number | Rarely | Built as a set: washer placed under the head, coating on the stated threads, packed and labelled as one item. |
| A coating zone, colour or product your drawing names | No | Zone, product and colour as specified; checked on the sample lot before the run. |
| M3 or M4 in A2 or A4 with a coating suited to small stainless threads | Seldom in the size you need | Small-thread coating versions on stainless; breakaway torque measured on your size. |
| Neutral packaging, your part number on the label, delivery to your customer | No | Done as standard for distributors: no EKINSUN name on the pack, your part number and quantity on the label, shipped to the address you give. |
| A certified safety-critical assembly with its own approval | — | We build to your specification and test the torque per lot; type approvals stay with the owner of the specification. |
What to Send for a Screw-and-Washer Set Price
The screw (standard, size, length, material or property class, head form), the washer (standard or d1 × d2 × h, material, captive or loose), the coating (product, or the breakaway torque the joint must reach, and the zone), packing and labelling, and the quantity per call-off and per year. A photo or a sample of the set you buy now is enough to start. Quote in 12 hours; approval drawing before the sample lot.
Pre-Applied Threadlocker Screws — Questions Buyers Ask
A dry coating put on the screw thread before delivery that does the job of a liquid threadlocker. In the microencapsulated type (DIN 267-27) the adhesive sits in capsules that break when the screw is tightened, so the joint cures in the hole; in the polyamide type (DIN 267-28) a nylon patch wedges the thread and holds by friction. The screw arrives ready to fit, with no bottle on the assembly line.
All three have a 3.2 mm hole for M3; they differ in outside diameter and thickness. DIN 433 (ISO 7092) is 3.2 × 6 × 0.5 mm and sits just outside the 5.5 mm head; DIN 125-A (ISO 7089) is 3.2 × 7 × 0.5 mm; DIN 9021 (ISO 7093-1) is 3.2 × 9 × 0.8 mm and has about 1.8 times the bearing area of DIN 125, for slotted holes, oversized holes, plastic and thin sheet.
Not by itself. Its 3.2 mm hole is larger than the 3 mm thread, so the washer slides off the end. A captive washer needs a hole smaller than the thread's outside diameter, put on the blank before the thread is rolled, which is how a SEMS screw is made. With a standard DIN 9021 washer the set is screw plus washer packed together, or the washer is fitted at assembly.
No. Unlike liquid threadlockers, pre-applied coatings carry no colour code across makers: the precote 80 datasheet lists the high-strength grade as red and states that colour is not a primary product feature, and special colours are made to order. Specify the product or the breakaway torque the joint must reach, not a colour.
Yes. DIN 267-27 covers steel and stainless screws from M3 to M39. Small threads need the small-thread version of a coating: precote 80-8 is the version for threads up to M6 or pitches up to 1 mm, and Henkel's selector recommends its P2 small microcapsules for fine threads, with DRI 204 and DRI 2045 listed as designed for plated and stainless fasteners. The breakaway torque on M3 is measured on a sample, because datasheet values are for M10.
EKINSUN — a custom fastener manufacturer in Shenzhen that builds screw, washer and pre-applied coating sets to a distributor's or OEM's specification: DIN 912 / ISO 4762 M3 to M8 in A2, A4 or steel, washers to DIN 433, 125, 9021 or a drawing, microencapsulated or nylon-patch coating, from a sample lot to tens of thousands of sets, in neutral packaging with the distributor's part number and delivery straight to the end customer. Quote in 12 hours.