EKINSUN is a custom parts manufacturer that turns socket head cap screws to drawing: a length between the standard steps or beyond them, a reduced or extended head, a fine, left-hand or inch thread, a size above M24, a material the catalogue does not carry, a drilled head for lock wire.
A typical request: M20 x 2.5 cap screws, 12.9, 185 mm long under the head, where stock goes 180 and 200 and the 200 fouls the casting.
Length is the first reason a cap screw is turned; the head and the pitch are the next two.
ISO 4762 / DIN 912 head sizes and hex keys
| Thread | Head diameter | Head height | Hex key | Coarse pitch |
|---|---|---|---|---|
| M3 | 5.5 mm | 3 mm | 2.5 mm | 0.5 |
| M4 | 7 mm | 4 mm | 3 mm | 0.7 |
| M5 | 8.5 mm | 5 mm | 4 mm | 0.8 |
| M6 | 10 mm | 6 mm | 5 mm | 1.0 |
| M8 | 13 mm | 8 mm | 6 mm | 1.25 |
| M10 | 16 mm | 10 mm | 8 mm | 1.5 |
| M12 | 18 mm | 12 mm | 10 mm | 1.75 |
| M14 | 21 mm | 14 mm | 12 mm | 2.0 |
| M16 | 24 mm | 16 mm | 14 mm | 2.0 |
| M20 | 30 mm | 20 mm | 17 mm | 2.5 |
| M24 | 36 mm | 24 mm | 19 mm | 3.0 |
Head diameter is 1.5 × d and head height equals d for every size in the table; the counterbore for a cap screw is sized from the head diameter plus clearance. Key sizes are the ISO 4762 values.
Need socket head cap screws in a size, thread or material no catalogue lists? EKINSUN is a custom parts manufacturer: we make socket head cap screws to your drawing, sketch or sample, steel up to class 12.9, 304 or 316L stainless steel or titanium, 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
Socket screw forms and size ranges
| Form | Standard | Size range | Common grades and materials | Notes |
|---|---|---|---|---|
| Socket head cap screw | ISO 4762 / DIN 912 | M1.4–M24 | 12.9 black M1.6–M24; 10.9 and 8.8 zinc M3–M20; A2 / A4 M1.4–M20; brass M3–M12; titanium M3–M12 | knurled or plain head; half thread from M4 |
| Fine-pitch cap screw | ISO 4762 (fine) | M3–M12 | A2 | M8×1, M10×1.25, M12×1.5 |
| Left-hand cap screw | maker series | M4–M16 | 12.9 black; A2 M6–M12 | counter-rotating spindles |
| Low head cap screw | DIN 7984 | M3–M16 | 12.9 black; 8.8 black; A2 | head about two thirds of ISO 4762 height; for shallow counterbores |
| Thin head cap screw | maker series | M2–M10 | A2; zinc steel | thinner still; sheet-metal covers |
| Button head screw | ISO 7380-1 | M1.6–M20 | 12.9 and 10.9 black; A2; brass M3–M12 | domed low head; keys 2–8 mm from M3 to M12 |
| Button head with flange | ISO 7380-2 | M3–M8 | A2; 10.9 | flange replaces the washer |
| Countersunk socket screw | ISO 10642 / DIN 7991 | M2–M24 | 12.9 and 10.9 black; A2; brass M3–M10 | 90° countersink; flush face |
| Truss (large flat) socket screw | maker series | M3–M8 | A2 | wide low head, socket drive |
| Socket cap with thread-locking patch | maker series | M2–M25 | 12.9; A2 | 180° or 360° nylon patch |
| Shoulder screw | ISO 7379 | M3–M16 | 12.9 | see shoulder bolts |
| Socket set screw | ISO 4026–4029 | M1.2–M24 | 12.9; A2 | see set screws |
Grades, keys and what breaks first
| Grade or material | Tensile class | Where it belongs | Watch |
|---|---|---|---|
| 12.9 black oxide | ISO 898-1 class 12.9 | machine tools, dies, high-preload joints | hydrogen embrittlement risk if plated; black oxide is the normal finish |
| 10.9 zinc or black | class 10.9 | general machinery | the class most zinc-plated cap screws are |
| 8.8 zinc | class 8.8 | frames, guards, covers | matches 8.8 hex bolts and class 8 nuts |
| A2-70 stainless | ISO 3506-1 A2-70 | outdoor, food, cleanroom | about class 8 strength; galling with A2 nuts without lubricant |
| A4-80 stainless | ISO 3506-1 A4-80 | marine, chemical | the strongest common stainless class |
| Brass, titanium | — | electrical, decorative, weight-critical | not for high preload; sized for the joint, not the class |
The hex socket is the weak point of the system: a rounded key or a worn socket strips before the thread does. Use the key size in the table, seat it fully, and on a cap screw that will be tightened often specify a Torx socket instead, the same screw with a star recess is a standard part to M20 and a custom one above.
What to send for a cap screw that is not in the box
- Thread and pitch; fine and left-hand are the commonest reason a cap screw is turned.
- Length under the head, and the thread length if the shank must be plain for a fit.
- Head: ISO 4762, low DIN 7984, button, countersunk, or a head diameter and height of your own.
- Grade or material: 12.9, 10.9, 8.8, A2, A4 / 316L, brass, titanium, 42CrMo4.
- Finish: black oxide, zinc, zinc-flake, plain stainless; a patch or a drilled head if wanted.
- Quantity; a single cap screw for a machine that is stopped is a normal order.
Read the pitch before you order the cap screw. 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
Will it clamp? Thread length and the half-threaded cap screw
An ISO 4762 / DIN 912 cap screw longer than a certain length is only threaded for part of its shank: the thread length is b = 2d + 12 mm, so 24 mm on an M6, 28 mm on an M8, 32 mm on an M10, 36 mm on an M12. The rest of the shank is plain, and the plain part is what stops the screw seating: if the parts being clamped are thinner than the plain length (l − b), the thread runout reaches the tapped hole before the head reaches the plate, and the head never pulls down. An M8×60 through a 20 mm plate is the classic case, 32 mm of plain shank, 12 mm of it trying to enter an M8 tapped hole. Fully threaded cap screws stop at 35 mm for M8, 40 mm for M10, 50 mm for M12 and 60 mm for M16; above that, a screw threaded to the head is a machined part.
What length do I need for a 20 mm plate into a tapped block?
For M8, a screw whose plain length is under 20 mm, M8×45 (17 mm plain) or shorter, with the thread reaching at least 1.5 × d into the block: M8×45 leaves 25 mm in the block, which is enough. If the design fixes the length at 60 mm, the answer is an M8×60 threaded to the head, which the box does not carry and we machine.
Same cap screw, but fully threaded, low head, or 130 mm long
Full thread past the catalogue limit, a DIN 7984 low head at the same thread, a length beyond the longest standard (80 mm for M8, 100 mm for M10, 120 mm for M12), a drilled head for lockwire, or A4 instead of 12.9: each is a variant of the same drawing, one piece and up, quoted in 12 hours.
Where the cap screw catalogue stops
| What you need | In the catalogue? | What we make |
|---|---|---|
| ISO 4762 cap screw M1.4–M24 in 12.9, 10.9, 8.8 or A2 / A4, standard length | Yes | Buy it from stock, or have it made to order from 1 piece. No one-off competes with a cold-formed and heat-treated cap screw. Standard parts: ask us too, we may have them in stock. |
| Low head DIN 7984 M3–M16, button ISO 7380 M1.6–M20, countersunk ISO 10642 M2–M24 | Yes | Standard sizes: buy them off the shelf, or have them made to order from 1 piece. Standard parts: ask us too, we may have them in stock. |
| A length between the standard steps, or longer than the longest standard length | No | Turned from bar in 42CrMo4 (class 12.9 territory after heat treatment), A2, 316L or brass, from 1 piece; length to the drawing. |
| A fine, left-hand or inch thread outside the standard sets | No | Single-pointed to your reading. |
| A cap screw above M24 — M27, M30, M36 | No | Turned from bar; see also large bolts and custom bolts. |
| A head of your own diameter or height, a drilled head for lock wire, a cross-drilled shank | No | Machined; see drilled head bolts. |
| A plain shank ground to a fit, a dog point, a reduced thread | No | Turned and ground; see shoulder bolts for the shouldered form. |
| A cap screw in aluminium 6061 or 7075 | Partly | 7075 cap screws are turned on request for weight-critical, low-preload joints and anodised; 6061 is too soft for a cap screw thread, and we say so. |
Materials
| Material | Designation | Where it fits here |
|---|---|---|
| Alloy steel class 12.9 | quenched and tempered, black oxide | the standard high-strength cap screw |
| Alloy steel | 42CrMo4 / 1.7225 | turned custom cap screws in 12.9 territory after heat treatment |
| Carbon steel class 8.8 / 10.9 | zinc plated | standard general-purpose cap screws |
| Stainless 304 | 1.4301 / A2-70 | standard stainless cap screws M1.4–M20 |
| Stainless 316L | 1.4404 / A4-80 | standard in the common sizes; turned above |
| Free-machining stainless | 303 / 1.4305 | custom turned cap screws where corrosion duty allows |
| Brass | CW614N / C36000 | standard M3–M12; turned above |
| Titanium | Grade 5 Ti6Al4V | standard M3–M12; turned above |
| Aluminium 7075 | AlZn5.5MgCu | turned light cap screws, anodised, low preload |
| Aluminium 6061 | AlMg1SiCu | not for cap screw threads; the alloy of the parts they clamp |
Related pages
- every fastener family by standard and size range, all families with standard and size range
- Wrench size chart, hex keys and across-flats for every size
- Metric bolt torque chart, torque for 8.8, 10.9 and 12.9
- Bolt grade chart, what the class numbers mean
- Clearance hole chart, hole sizes for cap screws
- Shoulder bolts, the shouldered socket screw
- Set screws, socket set screws
- Custom bolts, non-standard bolts of every form
Frequently asked questions
A 6 mm key. ISO 4762 keys run 2.5 mm for M3, 3 for M4, 4 for M5, 5 for M6, 6 for M8, 8 for M10, 10 for M12, 12 for M14, 14 for M16, 17 for M20 and 19 for M24. Button and countersunk socket screws take one size smaller.
One and a half times the thread diameter, and the head height equals the thread diameter: an M10 has a 16 mm head 10 mm high, an M12 an 18 mm head 12 mm high. The counterbore is sized from that diameter plus clearance.
12.9 is an alloy steel class with about twice the tensile strength of A2-70 stainless, which sits near class 8. Use 12.9 where preload matters and corrosion does not; use A2 or A4 where corrosion matters and the joint is sized for the lower strength.
Yes. Any length under the head, any thread length, and sizes above M24 are turned from 42CrMo4, A2, 316L, brass or titanium bar, from 1 piece, with the head to ISO 4762 or to your own dimensions.
EKINSUN is a custom parts manufacturer that turns socket head, low head, button and countersunk cap screws in alloy steel, 304 and 316L stainless, brass, titanium and aluminium 7075, in any pitch from M3 to M64, from 1 piece, with a quote within 12 hours.
No list price. The drivers are material, heat treatment, the head form, any drilling or grinding, and quantity. A batch of A2 cap screws in an odd length is a short lathe job; a single 12.9-territory M30 screw with a drilled head and a ground shank is priced as the machined part it is. The quote states which.
Send the thread, the length and the grade
Thread and pitch, length under the head, thread length, head form, grade or material, finish, quantity. A photo of the old screw on a rule works. From 1 piece, quote within 12 hours.