📐 Free Gage Block Calculator — no login. Open it →

← AskMachinist · Guides · Calculator · 🔎 Search

Domed Nylon Insert Lock Nut Dimensions (DIN 986, M4 to M16)

Guide · Updated October 28, 2026

DIN 986 covers prevailing torque hexagon domed cap nuts with a non-metallic (nylon) insert. Thread height m and overall height h agree across the Westfield Fasteners dome nyloc sheet, the MEAB stainless DIN 986 sheet and the Aspen Fasteners DIN 986 spec (M14 is in the first two only). Wrench size s agrees in all three for M4, M5, M6, M8 and M16; for M10 and M12 Westfield and MEAB list 16 / 18 mm while Aspen and the DIV Group sheet list 17 / 19 mm, so both are shown. Not shown: width across corners (the sources disagree at M4 and M5), fine-pitch rows and M20 (only one independent source). Check the current edition or your supplier for critical work.

Need an exact reference size?

Build any gage block stack with the free Gage Block Calculator. Free, no login.

Step by step

  1. Confirm the type: DIN 986 is a domed cap nut (acorn nut) with a nylon (polyamide) locking ring inside. It is the locking version of the DIN 1587 dome nut. This chart covers M4 to M16 coarse pitch.
  2. Pick the wrench: s is the wrench size: M4 7 mm, M5 8 mm, M6 10 mm, M8 13 mm, M16 24 mm. M10 and M12 come in both 16 / 18 mm and 17 / 19 mm widths depending on the maker, so measure or check the listing.
  3. Check the height: h is the overall height to the top of the dome: M6 12 mm, M8 14 mm, M10 18.1 mm, M12 22.5 mm, M16 27.5 mm.
  4. Check thread height: m is the height of the threaded section. The bolt must engage the full nylon ring to lock but must not hit the dome.
  5. Size the bolt: Bolt projection past the clamped parts should reach through the nylon ring but stay short of the dome. If the bolt bottoms out, the nut feels tight but gives no clamp load.
  6. Tighten: Run it on with a wrench (the nylon gives prevailing torque from the first turn), then torque as a regular nut of the same class. Nylon inserts are limited to about 120 C.

DIN 986 domed lock nut dimensions (mm)

Columns: thread size, coarse pitch P, wrench size s, thread height m, overall height h. Sizes in brackets are non-preferred.

Worked example: M8 domed lock nut

An M8 DIN 986 nut takes a 13 mm wrench and stands 14 mm tall, with 6.44 mm of thread height. Clamping a 15 mm stack plus a 1.6 mm washer, an M8 x 25 bolt leaves about 8.4 mm of projection: enough to pass through the nylon ring, and short enough to sit under the dome. An M8 x 30 leaves about 13.4 mm and is likely to hit the dome.

DIN 986 vs DIN 1587 vs ISO 7040

Common problems

FAQ

What is a DIN 986 nut?

A hex domed cap nut with a nylon insert: an acorn nut that also locks. The dome covers the bolt end and the nylon ring resists loosening from vibration.

How is DIN 986 different from DIN 1587?

DIN 1587 is the plain domed cap nut with no locking element. DIN 986 adds a nylon ring, so it has prevailing torque and resists backing off.

What wrench fits a DIN 986 M8 nut?

13 mm. M6 is 10 mm, M16 is 24 mm. M10 is 16 or 17 mm and M12 is 18 or 19 mm depending on the maker.

Can I reuse a DIN 986 nut?

A few times at most. The nylon loses grip each time; replace it if it spins on by hand.

What temperature can it take?

Polyamide inserts are usually rated to about 120 C. Use an all-metal lock nut for hotter jobs.

Is M14 standard?

It is a non-preferred size (in brackets) and harder to buy.

Related guides and calculators

Build your stack in seconds

The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.

Questions? Ask a machinist.

General shop information only — follow your drawing, tool maker's data and your quality system.