DIN 316 & ASME Wing Screws (Butterfly Screws): Manufacturer & Stockist
A butterfly screw has two flat wings instead of a drive. Finger and thumb turn it, so covers, guards, clamps and fixtures can be opened and closed again and again without looking for a tool.
Exotic Alloy manufactures butterfly screws in Mumbai, India, and keeps common sizes in stock for machine builders, furniture and display makers, and maintenance teams. We supply across India and export to Tanzania, East Africa, the Gulf and Europe.
Made for hand tightening
The wings give a long lever for the fingers, but they are not meant for spanners or pliers. Where a joint needs real preload, use a hex cap screw; for a smaller knob see knurled head screws and thumb screws.
DIN 316
DIN 318
ASME B18.6.8
Tool-free
A2 / A4, brass
Butterfly screw at a glance
- Also called
- Wing screw, wing bolt, thumb wing screw
- Metric
- DIN 316 rounded, DIN 318 edged
- Inch
- ASME B18.6.8 Types A–D
- Length
- From the bearing face
- Tightened
- By hand only
- Related
- Wing nuts, knurled, thumb screws
Butterfly Screw Specification
The range we manufacture and supply.
Metric standardsDIN 316 rounded wings; DIN 318 edged wings
Inch standardASME B18.6.8 (formerly B18.17), Types A, B, C, D
SizesM4–M24 (DIN 316), M4–M12 (DIN 318); No. 4 to 5/8 in
Lengths6–60 mm standard (DIN 316); longer to order
ThreadMetric coarse; UNC / UNF inch
WingsRounded, edged; light, regular, heavy (Type A)
MaterialsSteel; brass; stainless A2 / A4
FinishZinc plated; stainless and brass plain
CertificationMill certificate; EN 10204 3.1 on request
PackingBoxes of 50 to 1,000; bulk cartons
Rounded, Edged & ASME Type A to D Wings
Two metric wing shapes and six inch types and styles.
| Type | Make | Sizes | Spread A, 1/4 in size max, in | Height B, 1/4 in size max, in | Wing thickness C 1/4 in size, max |
|---|---|---|---|---|---|
| Type A | cold forged, light / regular / heavy wings | No. 4 to 5/8 | 1.25 (regular) | .66 | .21 |
| Type B, style 1 | round nose, steel (UNS G10060) | No. 10 to 5/8 | 1.16 | .56 | .17 |
| Type B, style 2 | high head and round nose | No. 10 to 3/8 | 1.22 | .94 | .16 |
| Type C, style 1 | die cast, zinc alloy (UNS Z33520) | No. 6 to 3/8 | 1.08 | .56 | .17 |
| Type C, style 2 | zinc alloy (UNS Z33520) or steel (UNS G10060) | No. 6 to 1/2 | 1.08 | .57 | .16 |
| Type D | stamped from steel sheet (UNS G10060) | No. 6 to 3/8 | 1.09 | .46 | .26 |
ASME B18.6.8-2010. Make and material from the standard’s table titles; values in inches.
Wing Screw Dimensions
| Size | Wing span e max / min | Head height h max / min | Boss d2 bearing, max / min | Boss d3 top, max / min | Boss height m max / min | Wing g / G tip / root, min | a max under head |
|---|---|---|---|---|---|---|---|
| M4 × 0.7 | 20 / 18 | 10.5 / 8.5 | 8 / 6 | 7 / 5.5 | 4.6 / 3.2 | 1.1 / 1.7 | 2.1 |
| M5 × 0.8 | 26 / 24 | 13 / 11 | 11 / 8 | 9 / 7.5 | 6.5 / 4 | 1.5 / 2.3 | 2.4 |
| M6 × 1 | 33 / 30 | 17 / 15 | 13 / 10 | 11 / 9 | 8 / 5 | 1.5 / 2.7 | 3 |
| M8 × 1.25 | 39 / 36 | 20 / 18 | 16 / 13 | 12.5 / 10.5 | 10 / 6.5 | 2 / 3.6 | 4 |
| M10 × 1.5 | 51 / 48 | 25 / 23 | 20 / 17 | 16.5 / 14.5 | 12 / 8 | 3.6 / 4.6 | 4.5 |
| M12 × 1.75 | 65 / 62 | 33.5 / 31 | 23 / 20 | 19.5 / 17.5 | 14 / 10 | 4.1 / 5.6 | 5.3 |
| M16 × 2 | 73 / 70 | 37.5 / 35 | 29 / 26 | 23 / 21 | 17 / 13 | 5.6 / 6.5 | 6 |
| M20 × 2.5 | 90 / 86 | 46.5 / 44 | 35 / 32 | 29 / 27 | 21 / 16 | 6.1 / 7 | 7.5 |
| M24 × 3 | 110 / 106 | 56.5 / 53.5 | 44 / 41 | 37.5 / 35 | 25 / 20 | 8.6 / 9.5 | 9 |
DIN 316, mm (1983, 1998 and 2016 editions give the same values). Bold: the M12 head height max is 33.5 here and 35.5 in the DIN 315 wing nut.
| Length l | M4 | M5 | M6 | M8 | M10 | M12 | M16 | M20 | M24 |
|---|---|---|---|---|---|---|---|---|---|
| 6 | |||||||||
| 8 | |||||||||
| 10 | |||||||||
| 12 | |||||||||
| 14 | |||||||||
| 16 | |||||||||
| 18 | |||||||||
| 20 | |||||||||
| 25 | |||||||||
| 30 | |||||||||
| 35 | |||||||||
| 40 | |||||||||
| 45 | |||||||||
| 50 | |||||||||
| 60 |
DIN 316 commercial lengths, mm, measured from the bearing face. Other lengths to order.
| Size | Wing span n, max / min | Head height H, max / min | Boss dk, max / min | Boss height k, max / min | DIN 316 span for comparison |
|---|---|---|---|---|---|
| M4 | 21 / 19 | 11 / 9 | 9 / 7 | 4.6 / 3.2 | 20 / 18 |
| M5 | 26.5 / 24.5 | 13 / 11 | 12 / 9 | 6 / 4 | 26 / 24 |
| M6 | 32 / 29 | 16 / 14 | 14 / 11 | 7 / 5 | 33 / 30 |
| M8 | 38 / 35 | 19 / 17 | 16 / 13 | 8.5 / 6.5 | 39 / 36 |
| M10 | 50 / 47 | 24 / 22 | 21 / 18 | 10 / 8 | 51 / 48 |
| M12 | 66 / 63 | 32 / 29 | 24 / 21 | 13 / 10 | 65 / 62 |
DIN 318 (1999 / 2016), mm.
| Size & series | Threads per inch | Spread A max / min | Height B max / min | Wing thickness C max / min | Boss dia. max / min | Boss height max / min | Lengths min–max |
|---|---|---|---|---|---|---|---|
| No. 4 Heavy | 40 | .72 / .59 | .41 / .28 | .11 / .07 | .33 / .29 | .14 / .10 | .25–.75 |
| No. 6 Light | 32 | .72 / .59 | .41 / .28 | .11 / .07 | .33 / .29 | .14 / .10 | .25–.75 |
| No. 6 Heavy | 32 | .91 / .78 | .47 / .34 | .14 / .10 | .43 / .39 | .18 / .14 | .25–.75 |
| No. 8 Light | 32 | .91 / .78 | .47 / .34 | .14 / .10 | .43 / .39 | .18 / .14 | .38–.75 |
| No. 8 Heavy | 32 | 1.10 / .97 | .57 / .43 | .18 / .14 | .50 / .45 | .22 / .17 | .38–.75 |
| No. 10 Light | 24, 32 | .91 / .78 | .47 / .34 | .14 / .10 | .43 / .39 | .18 / .14 | .38–1.00 |
| No. 10 Heavy | 24, 32 | 1.10 / .97 | .57 / .43 | .18 / .14 | .50 / .45 | .22 / .17 | .38–1.00 |
| No. 12 Light | 24 | 1.10 / .97 | .57 / .43 | .18 / .14 | .50 / .45 | .22 / .17 | .38–1.00 |
| No. 12 Heavy | 24 | 1.25 / 1.12 | .66 / .53 | .21 / .17 | .58 / .51 | .25 / .20 | .38–1.50 |
| 1/4 Light | 20 | 1.10 / .97 | .57 / .43 | .18 / .14 | .50 / .45 | .22 / .17 | .50–1.50 |
| 1/4 Regular | 20 | 1.25 / 1.12 | .66 / .53 | .21 / .17 | .58 / .51 | .25 / .20 | .50–1.50 |
| 1/4 Heavy | 20 | 1.44 / 1.31 | .79 / .65 | .24 / .20 | .70 / .64 | .30 / .26 | .50–1.50 |
| 5/16 Light | 18 | 1.25 / 1.12 | .66 / .53 | .21 / .17 | .58 / .51 | .25 / .20 | .50–1.50 |
| 5/16 Regular | 18 | 1.44 / 1.31 | .79 / .65 | .24 / .20 | .70 / .64 | .30 / .26 | .50–1.50 |
| 5/16 Heavy | 18 | 1.94 / 1.81 | 1.00 / .87 | .33 / .26 | .93 / .86 | .39 / .35 | .50–1.50 |
| 3/8 Light | 16 | 1.44 / 1.31 | .79 / .65 | .24 / .20 | .70 / .64 | .30 / .26 | .75–2.00 |
| 3/8 Regular | 16 | 1.94 / 1.81 | 1.00 / .87 | .33 / .26 | .93 / .86 | .39 / .35 | .75–2.00 |
| 3/8 Heavy | 16 | 2.76 / 2.62 | 1.44 / 1.31 | .40 / .34 | 1.19 / 1.13 | .55 / .51 | .75–2.00 |
| 7/16 Light | 14 | 1.94 / 1.81 | 1.00 / .87 | .33 / .26 | .93 / .86 | .39 / .35 | 1.00–4.00 |
| 7/16 Heavy | 14 | 2.76 / 2.62 | 1.44 / 1.31 | .40 / .34 | 1.19 / 1.13 | .55 / .51 | 1.00–4.00 |
| 1/2 Light | 13 | 1.94 / 1.81 | 1.00 / .87 | .33 / .26 | .93 / .86 | .39 / .35 | 1.00–4.00 |
| 1/2 Heavy | 13 | 2.76 / 2.62 | 1.44 / 1.31 | .40 / .34 | 1.19 / 1.13 | .55 / .51 | 1.00–4.00 |
| 5/8 Heavy | 11 | 2.76 / 2.62 | 1.44 / 1.31 | .40 / .34 | 1.19 / 1.13 | .55 / .51 | 1.25–4.00 |
ASME B18.6.8-2010 Type A, inch (same as B18.17-1968 except the No. 12 Heavy length range, now up to 1.50 in).
| Type | Size | Threads per inch | Spread A max / min | Height B max / min | Wing thickness C max / min | Lengths min–max |
|---|---|---|---|---|---|---|
| Type B, style 1 | No. 10 | 24 | .97 / .91 | .45 / .39 | .15 / .12 | .50–2.00 |
| Type B, style 1 | 1/4 | 20 | 1.16 / 1.09 | .56 / .50 | .17 / .14 | .50–3.00 |
| Type B, style 1 | 5/16 | 18 | 1.44 / 1.38 | .67 / .61 | .18 / .15 | .50–3.00 |
| Type B, style 1 | 3/8 | 16 | 1.72 / 1.66 | .80 / .73 | .20 / .17 | .50–4.00 |
| Type B, style 1 | 7/16 | 14 | 2.00 / 1.94 | .91 / .84 | .21 / .18 | 1.00–3.00 |
| Type B, style 1 | 1/2 | 13 | 2.31 / 2.22 | 1.06 / .94 | .23 / .20 | 1.00–3.00 |
| Type B, style 1 | 5/8 | 11 | 2.84 / 2.72 | 1.31 / 1.19 | .27 / .23 | 1.00–2.50 |
| Type B, style 2 | No. 10 | 24 | 1.01 / .95 | .78 / .72 | .14 / .11 | .50–1.25 |
| Type B, style 2 | 1/4 | 20 | 1.22 / 1.16 | .94 / .88 | .16 / .13 | .50–2.00 |
| Type B, style 2 | 5/16 | 18 | 1.43 / 1.37 | 1.09 / 1.03 | .17 / .14 | .50–2.00 |
| Type B, style 2 | 3/8 | 16 | 1.63 / 1.57 | 1.25 / 1.19 | .18 / .15 | .50–2.00 |
| Type C, style 1 | No. 6 | 32 | .85 / .83 | .45 / .43 | .15 / .12 | .25–.75 |
| Type C, style 1 | No. 8 | 32 | .85 / .83 | .45 / .43 | .15 / .12 | .38–1.00 |
| Type C, style 1 | No. 10 | 24, 32 | .85 / .83 | .45 / .43 | .15 / .12 | .38–1.25 |
| Type C, style 1 | 1/4 | 20 | 1.08 / 1.05 | .56 / .53 | .17 / .14 | .50–1.50 |
| Type C, style 1 | 5/16 | 18 | 1.23 / 1.20 | .64 / .62 | .22 / .19 | .50–1.50 |
| Type C, style 1 | 3/8 | 16 | 1.45 / 1.42 | .74 / .72 | .24 / .21 | .50–1.50 |
| Type C, style 2 | No. 6 | 32 | .85 / .83 | .43 / .42 | .14 / .12 | .25–1.00 |
| Type C, style 2 | No. 8 | 32 | .85 / .83 | .43 / .42 | .14 / .12 | .38–1.00 |
| Type C, style 2 | No. 10 | 24, 32 | .85 / .83 | .43 / .42 | .14 / .12 | .38–2.00 |
| Type C, style 2 | 1/4 | 20 | 1.08 / 1.05 | .57 / .53 | .16 / .14 | .50–2.50 |
| Type C, style 2 | 5/16 | 18 | 1.23 / 1.20 | .64 / .62 | .20 / .18 | .50–3.00 |
| Type C, style 2 | 3/8 | 16 | 1.45 / 1.42 | .74 / .72 | .23 / .21 | .75–3.00 |
| Type C, style 2 | 7/16 | 14 | 1.89 / 1.86 | .91 / .90 | .29 / .28 | 1.00–4.00 |
| Type C, style 2 | 1/2 | 13 | 1.89 / 1.86 | .91 / .90 | .29 / .28 | 1.00–4.00 |
| Type D | No. 6 | 32 | .78 / .72 | .40 / .34 | .18 / .12 | .25–.75 |
| Type D | No. 8 | 32 | .78 / .72 | .40 / .34 | .18 / .12 | .38–.75 |
| Type D | No. 10 | 24 | .90 / .84 | .46 / .40 | .21 / .15 | .38–1.00 |
| Type D | No. 12 | 24 | 1.09 / 1.03 | .46 / .40 | .26 / .20 | .38–1.00 |
| Type D | 1/4 | 20 | 1.09 / 1.03 | .46 / .40 | .26 / .20 | .50–1.50 |
| Type D | 5/16 | 18 | 1.31 / 1.25 | .62 / .56 | .29 / .23 | .50–1.50 |
| Type D | 3/8 | 16 | 1.31 / 1.25 | .62 / .56 | .29 / .23 | .75–2.00 |
ASME B18.6.8-2010, inch. Boss sizes for these types on request.
Wing Screws & Wing Nuts Share One Head
A DIN 316 screw is, in effect, a DIN 315 wing nut on a shank: span e, boss d2, boss height m and wing thickness g are identical. The edged DIN 318 screw matches the DIN 314 wing nut in the same way.
So a design can use a wing screw on one side and a wing nut on a stud elsewhere and both need the same swing room. Wing nuts are on our nuts page.
| Wing screw | Same head as | Wings | Sizes |
|---|---|---|---|
| DIN 316 | DIN 315 wing nut | Rounded | M4–M24 |
| DIN 318 | DIN 314 wing nut | Edged | M4–M12 |
Only exception found: DIN 316 M12 head height max 33.5 mm, DIN 315 M12 35.5 mm.
Swing Room & Hand Torque
- Room to turn: keep walls and flanges at least half the span from the axis, plus room for fingers.
- Finger tight: a wider span gives more torque for the same finger force.
- No tools: pliers and spanners bend the wings.
- Washer: a plain washer under the boss protects painted or soft parts.
| Need | Better choice |
|---|---|
| Hand tightening, frequent opening | Butterfly screw |
| Hand tightening, low profile | Knurled head screw |
| Controlled preload | Hex cap screw and a torque wrench |
| Panel that must not be opened casually | A screw that needs a tool |
Wing Screw Clearance & Hand Torque Finder
Check the swing room and see what a given hand torque means for finger force and clamp.
Screw & space
Our calculation. Swing diameter = maximum span. Finger force: two fingers pushing the wing tips as a couple, F = T / e (mean span). Clamp force: rule of thumb F = T / (0.2 d). Thread stress = clamp / stress area As (ISO 898-1, ASME B1.1), shown against the 240 MPa yield of steel class 4.6 for reference. The wings, not the thread, usually limit hand torque; we do not publish a wing strength rating.
Result
39
mm swing diameter
26.7
N per finger
Room beyond the wing tips:10.5 mm
Clamp force (rule of thumb):625 N
Thread stress:17.1 MPa (7 % of 240)
Designation:DIN 316 M8
Butterfly Screw Materials & Finishes
| Material | Allowed by | Finish | Where |
|---|---|---|---|
| Steel, forged or cold worked | DIN 316; ASME (UNS G10060) | Zinc plated | Indoor machinery and fixtures |
| Stainless A2 / A4 | DIN 316 (austenitic) | Plain | Outdoor, food, marine (as in the photo) |
| Brass | DIN 316 (CuZn) | Natural | Electrical, decorative |
| Malleable cast iron | DIN 316 (GTS / GTW) | Plain or plated | Large sizes, to order |
| Zinc die-casting alloy | ASME Type C (UNS Z33520) | Plain or plated | Light-duty inch screws, to order |
DIN 316 leaves the grade within each material group to the manufacturer.
How Our Butterfly Screws Are Made
1
Material
Wire or bar, certified by heat.
2
Forming
Wings cold forged or forged; cast or stamped types to order.
3
Trimming
Flash removed, wing edges rounded.
4
Thread
Thread rolled on the shank.
5
Finishing
Zinc plating, or cleaning and passivation.
6
Packing
Counted boxes, lot-labelled.
Where Our Butterfly Screws Are Used
Machine guards
Covers opened for cleaning and setting.
Jigs & fixtures
Stops, fences and quick clamps.
Food machinery
Stainless screws on parts removed for washdown.
Displays & stands
Exhibition stands and signage.
Music & camera stands
Height and angle adjusters.
Electrical
Battery terminals and test fixtures in brass.
Butterfly Screw Inspection & Certification
| Check | Method | Applied to |
|---|---|---|
| Span e, height h | Callipers to DIN / ASME | Every lot |
| Wing thickness, boss | Callipers | Every lot |
| Wing symmetry, burrs | Visual | Every lot |
| Thread | Ring gauges | Every lot |
| Length, a max | Height gauge | Every lot |
| Material | PMI / chemical analysis | Stainless and brass |
Every shipment includes
- Mill certificate with heat number
- Dimensional report
- Lot number on every box
On request
- EN 10204 3.1 certificate
- Salt spray test for plated lots
- RoHS declaration
Butterfly Screw Questions, Answered
A butterfly screw, or wing screw, is a screw with two flat wings on its head so it can be turned by hand, without a tool. Metric wing screws are standardised in DIN 316 with rounded wings (M4 to M24) and DIN 318 with edged wings (M4 to M12); inch wing screws in ASME B18.6.8, Types A to D.
The wing shape. DIN 316 has rounded wings and shares its head sizes with the DIN 315 wing nut; DIN 318 has edged, straight-cut wings and shares its head sizes with the DIN 314 wing nut. For M6 the span is 30 to 33 mm in DIN 316 and 29 to 32 mm in DIN 318.
From the bearing face under the boss to the end of the screw; the wings are not included. Under the head DIN 316 allows an unthreaded length of up to 2.1 mm for M4, rising to 9 mm for M24.
They describe how the screw is made and the wing form in ASME B18.6.8: Type A is cold forged with light, regular and heavy wings, Type B has round-nose wings (style 2 with a high head), Type C style 1 is die cast in zinc alloy and Type D is stamped from steel sheet.
By hand only. The torque is the finger force at the wing tips times the span: two fingers pushing with 27 N each on an M8 DIN 316 screw, span about 37.5 mm, give about 1 N m. Do not use pliers or a spanner, which bend the wings; if the joint needs more clamp, use a hex head screw.
A full circle as wide as the wing span, plus room for the fingers. For an M8 DIN 316 screw the span is up to 39 mm, so anything closer than 19.5 mm to the screw axis stops the wings turning.
Yes. A DIN 316 screw has the wing span, boss and wing thickness of the DIN 315 wing nut, and a DIN 318 screw those of the DIN 314 nut, so a wing screw and a wing nut of the same thread look alike and need the same room to turn.
DIN 316 allows malleable cast iron, steel (forged or cold worked), brass and austenitic stainless steel. We make wing screws in zinc-plated steel, brass and A2 or A4 stainless; the screw in our photo is stainless.