EKINSUN is a custom parts manufacturer that turns cap nuts and sleeve nuts to drawing: a deeper thread for a long bolt, a taller or slimmer dome, a polished or plated finish, a fine or left-hand pitch, a size above M30, a material the catalogue skips. The size ranges are those a distributor stocked in 2026.
A typical request: stainless dome nuts M10 for a handrail whose studs are 4 mm too long, so the domes bottom out before the hex touches.
Thread depth under the dome is the number nobody prints on the box.
Cap nut types and size ranges
| Type | Standard | Size range | Common materials | Notes |
|---|---|---|---|---|
| High cap nut, one-piece dome | DIN 1587 | M2–M30 | 304 stainless; brass M3–M20; zinc, nickel, black and plain steel M3–M16 | the standard acorn nut: tallest dome, deepest thread |
| Low cap nut | DIN 917 | M3–M16 | 304 | shorter dome where space is tight; less thread depth |
| Dome nyloc nut | DIN 986 | M5–M12 | 304 | prevailing torque and a closed end in one part |
| All-metal dome lock nut | maker series | M5–M12 | 304 | closed end with metal locking; heat and chemicals |
| Fine-pitch cap nut | maker series | M8–M16 | 304 | M8×1, M10×1.25, M12×1.5, M16×1.5 |
| Left-hand cap nut | maker series | M6–M16 | 304 | counter-rotating shafts and rollers |
| Two-piece welded dome nut | maker series | M3–M16 | steel, zinc plated | a hex nut with a pressed cap welded on; cheaper, not for polished work |
| White-capped or coloured protective cap | maker series | M3–M24 caps; M5–M10 white-capped nuts | PE / nylon caps on steel or 304 nuts | cosmetic and finger protection on fences, playgrounds, appliances |
| Nylon cap nut | — | M3–M20 | nylon 66, white and black | insulating; see plastic fasteners |
Need cap nuts in a size, thread or material no catalogue lists? EKINSUN is a custom parts manufacturer: we make cap nuts to your drawing, sketch or sample, brass, steel, 304 or 316L stainless steel, from 1 piece, quoted in 12 hours and shipped duties paid. Standard sizes can often be supplied from stock; the more pieces, the lower the unit price. All custom fasteners
How far the bolt may reach: thread depth under the dome
Every cap nut has a threaded length and a dome cavity above it. The bolt must stop inside the threaded length; if it runs into the dome it either bottoms before the nut seats, the joint is loose and looks tight, or it pushes the dome off a two-piece nut. The rule is simple: bolt protrusion beyond the mating face must be shorter than the nut's thread depth, and DIN 1587 lists that depth per size. In practice:
- High DIN 1587 nuts take the longest bolt end; low DIN 917 nuts the shortest.
- A two-piece welded dome has less depth than a one-piece dome of the same size.
- A dome nyloc DIN 986 loses some depth to the nylon ring.
- When the bolt cannot be shortened, a stud in a casting, a handrail spigot, a machine that is already built, the cap nut is turned with a deeper thread or a taller dome, and the outside stays a standard acorn.
Read the pitch before you order the cap nut. Lay a steel rule along ten thread crests and divide by ten: 10 mm over ten pitches is a 1 mm pitch (M6 coarse), 12.5 mm is M8 coarse, 15 mm is M10 coarse, 17.5 mm is M12 coarse. A reading that is not a round number of millimetres is an inch thread, and a reading that is shorter than the coarse pitch for that diameter is a fine thread. If diameter, pitch and the size range in the table all agree, the part is a standard size: buy it off the shelf, or have it made to order from 1 piece. If any of the three falls outside the table, we make it to your reading. The full measuring routine, including the inch traps
Where the cap nut catalogue stops
| What you need | In the catalogue? | What we make |
|---|---|---|
| DIN 1587 cap nut M2–M30 in 304, or M3–M16 in zinc steel, coarse pitch | Yes | Buy it from stock, or have it made to order from 1 piece. No one-off competes with a formed dome nut, and 304 domes are standard to M30. Standard parts: ask us too, we may have them in stock. |
| Brass cap nut M3–M20 | Yes | Standard sizes: buy them off the shelf, or have them made to order from 1 piece. Nickel or chrome plating over brass on request. Standard parts: ask us too, we may have them in stock. |
| A cap nut with a thread deep enough for a bolt that cannot be shortened | No | Turned from bar with the thread depth you need and a standard dome outside; from 1 piece. |
| A taller, slimmer or wider dome than DIN: for a handrail, a lamp, an instrument | No | Turned to the profile; polished, brushed or plated. |
| Fine-pitch or left-hand outside the standard sets, or any pitch above M16 | No | Tapped or single-pointed to your reading. |
| A cap nut above M30, or in 316L / 1.4404, titanium or 42CrMo4 | No | Turned from bar; certificates per batch where the drawing calls for them. |
| A sleeve nut: a long closed nut joining two studs, or capping a long thread | No | Turned; internal thread to the full length you specify. |
| A cap nut in aluminium 6061 or 7075 | Partly | Anodised aluminium cap and cup washers M2–M8 are standard; aluminium cap nuts are turned on request and not offered for high preload. |
Materials
| Material | Designation | Where it fits here |
|---|---|---|
| Stainless 304 | 1.4301 / A2 | the standard cap nut M2–M30; outdoor, handrails, food equipment |
| Stainless 316L | 1.4404 / A4 | turned to order for marine and pool fittings |
| Free-machining stainless | 303 / 1.4305 | custom turned and polished domes |
| Brass | CW614N / C36000 | standard M3–M20; nickel or chrome plated for decorative work |
| Carbon steel | zinc, nickel, black oxide, plain | standard M3–M16; one-piece and welded |
| Alloy steel | 42CrMo4 / 1.7225 | turned cap and sleeve nuts for machine spindles |
| Aluminium 6061 | AlMg1SiCu | turned light cap nuts for low-load, decorative or weight-critical parts |
| Aluminium 7075 | AlZn5.5MgCu | anodised cap and cup washers M2–M8 as standard parts; turned nuts on request |
| Titanium | Grade 5 Ti6Al4V | turned dome nuts for motorcycle and race parts |
| Nylon 66, PE | PA66, PE | insulating cap nuts M3–M20; protective caps M3–M24 |
Related pages
- the nut, bolt, washer and pin chart, all families with standard and size range
- flange nuts: when the base, not the top, is the problem
- Tall and thin nuts, open nuts in non-standard heights
- Knurled nuts, hand-tightened decorative nuts
- Large custom nuts, M30 and up
- Titanium bolts, the matching titanium hardware
- Hutmutter-Tabelle DIN 1587 / 917, German: across-flats old and new (M10 16 or 17), height and thread depth M4–M24
Frequently asked questions
Nothing: they are three names for the same closed-end nut. DIN 1587 is the high one-piece form most people mean; DIN 917 is a low cap; a dome nyloc DIN 986 adds a nylon locking ring under the dome.
Shorter than the nut's thread depth, measured from the mating face; DIN 1587 lists the depth per size. If the bolt reaches into the dome the nut bottoms before it seats and the joint is loose. When the bolt cannot be shortened, the cap nut is turned with a deeper thread.
As standard parts: fine pitch M8–M16 and left-hand M6–M16 in 304. Other sizes, pitches and materials are turned and tapped to order from 1 piece.
Yes. Standard 304 domes are bright-finished; brass domes take nickel or chrome; turned domes in 303 or 316L are polished to the finish you specify, which is one reason decorative cap nuts are made rather than bought.
EKINSUN is a custom parts manufacturer that turns cap nuts, dome nuts and sleeve nuts in 304 and 316L stainless, brass, steel, aluminium and titanium, from M3 to M64, in any pitch, from 1 piece, with a quote within 12 hours.
There is no list price. The drivers are material, thread depth and dome profile, polishing, and quantity. A batch of 304 cap nuts with a deeper thread is a short lathe job; a single polished 316L dome above M30 is priced as the turned and polished part it is. The quote states the drivers.
Send the thread and the bolt protrusion
Thread and pitch, how far the bolt reaches beyond the face, dome height or diameter if it matters, finish, material, quantity. A photo of the stud with a rule works. From 1 piece, quote within 12 hours.