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Allmat Group
Socket Button Screw

304 (A2) · 316 (A4) · A4-80 · Alloy Steel · Class 10.9 · Class 12.9 · Class 8.8

Socket Button Screw

Socket button head screws (button head cap screws) in steel, 304 and 316 stainless and zinc flake, metric and imperial.

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About the Socket Button Screw

Button head screws have a low, rounded head for a neat finish where a bolt head should not stick out, on guards, covers, panels, car and bike parts and machinery trim. They come to ISO 7380 from M3 to M16 and in #4 to 5/8 inch UNC, UNF and BSW: class 10.9 and 12.9 alloy steel (plain, zinc plated or zinc flake), zinc plated class 8.8, imperial alloy steel (ASTM F835), and 304 and 316 stainless with a hex socket or Torx drive. Choose the material, size and length above; the guide below covers why they are not a full strength bolt, sizes and torques.

Also called button head bolts, dome head bolts or button head socket screws.

Features

  • Low domed button head
  • Hex-key and Torx drive
  • High-tensile and stainless
  • ISO 7380

Applications

  • Guards, covers and panels on machinery
  • Car, bike and trailer accessories
  • Anywhere a low, neat head is needed

What is a button head screw?

A button head socket screw has a low, rounded head with a flat bearing face, driven by a hex key (Allen key) or Torx bit. Hobson describes button heads as sitting slightly proud of the work piece and being used for appearance, so they suit guards, covers, panels, brackets, trim and anywhere a smooth, low head looks neater or there is little clearance. People also call them button head bolts, dome head bolts or button head cap screws.

Torx drive (304 stainless, M8 to M12) has a six-point star recess that Hobson says increases the torque you can apply, prevents cam out and helps the screw last. Hobson's sheet gives T40 for M8, T50 for M10 and T55 for M12.

Button heads are reduced strength: the 010.9 and 012.9 marks

A button head is not a full strength bolt. Hobson's Soko guide explains that countersunk, button head and low head socket screws have reduced loadability because the stress area in the head is smaller than in the thread, and their head marks carry a leading 0: 08.8, 010.9 and 012.9 instead of 8.8, 10.9 and 12.9. They are tightened to lower torques than a socket head cap screw of the same class (see below).

Where a joint needs the full strength of the class, use a socket head cap screw or hex bolt instead. Hobson publishes no load ratings for these button head screws, so do not use them for structural or safety critical joints unless an engineer has specified them.

Metric button head screw sizes and lengths

Every metric button head screw we carry, by material, smallest to largest. Lengths are measured under the head. Select a row to open that size in the selector, then pick the length.

Metric button head socket screws to ISO 7380, coarse thread. Lengths in mm under the head. Pack is the minimum order quantity. Hex socket drive unless shown as Torx. Tap a number to show it in the selector above.

SizeMaterial and classLengths (mm)Pack
Plain alloy steel, class 10.9
M4Plain alloy steel, class 10.98, 10, 12, 16100
M5Plain alloy steel, class 10.910, 12, 16, 20, 25100
M6Plain alloy steel, class 10.910, 12, 16, 20, 25, 30, 35100
M8Plain alloy steel, class 10.910, 12, 16, 20, 25, 30, 35, 40, 50100
M10Plain alloy steel, class 10.920, 25, 30, 35100
Zinc plated, class 10.9
M4Zinc plated, class 10.912, 16, 20, 25100
M5Zinc plated, class 10.910, 12, 16, 20, 25, 35100
M6Zinc plated, class 10.910, 12, 16, 20, 25, 30, 35, 40, 50100
M8Zinc plated, class 10.910, 12, 16, 20, 25, 30, 35, 40, 45, 50100
M10Zinc plated, class 10.916, 20, 25, 30, 35, 40, 50, 60, 7050 to 100
M12Zinc plated, class 10.920, 25, 30, 35, 40, 50, 60, 7050 to 100
Zinc plated, class 8.8
M6Zinc plated, class 8.816200
M8Zinc plated, class 8.816200
Plain alloy steel, class 12.9
M3Plain alloy steel, class 12.96, 8, 10, 12, 16, 20100
M4Plain alloy steel, class 12.98, 10, 12, 16, 20, 25100
M5Plain alloy steel, class 12.96, 8, 10, 12, 16, 20, 25, 30, 35, 40100 to 200
M6Plain alloy steel, class 12.910, 12, 16, 20, 25, 30, 35, 40, 45, 50100
M8Plain alloy steel, class 12.910, 12, 16, 20, 25, 30, 35, 40, 45, 50100
M10Plain alloy steel, class 12.916, 20, 25, 30, 35, 40, 45, 5050 to 100
M12Plain alloy steel, class 12.916, 20, 25, 30, 35, 40, 45, 50, 60, 7050 to 100
M16Plain alloy steel, class 12.97025
Zinc plated, class 12.9
M4Zinc plated, class 12.98, 10, 12, 16, 20, 25100
M5Zinc plated, class 12.96, 8, 10, 12, 16, 20, 25, 30, 35, 40100
M6Zinc plated, class 12.910, 12, 16, 20, 25, 30, 35, 40, 45, 50, 65100
M8Zinc plated, class 12.910, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 75, 80100
M10Zinc plated, class 12.916, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 10050 to 100
M12Zinc plated, class 12.920, 25, 30, 35, 40, 50, 60, 70, 80, 10050 to 100
M16Zinc plated, class 12.96025
Zinc flake silver, class 12.9
M3Zinc flake silver, class 12.98100
M4Zinc flake silver, class 12.920100
M5Zinc flake silver, class 12.910, 16100
M6Zinc flake silver, class 12.916, 20, 30100 to 200
M8Zinc flake silver, class 12.916, 20, 25100 to 200
M10Zinc flake silver, class 12.925, 5050 to 100
M12Zinc flake silver, class 12.925, 35100
304 stainless, hex socket, A2
M3304 stainless, hex socket, A24, 5, 6, 8, 10, 12, 16, 20, 25, 30, 40, 50100
M4304 stainless, hex socket, A24, 5, 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50100
M5304 stainless, hex socket, A26, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60100
M6304 stainless, hex socket, A28, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 8050 to 100
M8304 stainless, hex socket, A210, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 10050 to 100
M10304 stainless, hex socket, A216, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 10050
M12304 stainless, hex socket, A216, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 10025
M16304 stainless, hex socket, A25025
304 stainless, Torx, A2
M8304 stainless, Torx, A212, 16, 20, 25, 30, 35, 40, 50, 7050 to 100
M10304 stainless, Torx, A216, 20, 25, 30, 40, 5050
M12304 stainless, Torx, A225, 30, 35, 40, 5025
316 stainless, hex socket, A4
M3316 stainless, hex socket, A45, 6, 8, 10, 12, 16, 20, 25, 30100
M4316 stainless, hex socket, A46, 8, 10, 12, 16, 20, 25, 30, 35, 40100
M5316 stainless, hex socket, A48, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 60100
M6316 stainless, hex socket, A48, 10, 12, 16, 20, 25, 30, 35, 40, 50, 6050 to 100
M8316 stainless, hex socket, A410, 12, 16, 20, 25, 30, 35, 40, 50, 60, 7050 to 100
M10316 stainless, hex socket, A416, 20, 25, 30, 35, 40, 50, 6050
M12316 stainless, hex socket, A420, 25, 30, 35, 40, 50, 6025

Imperial button head screws: UNC, UNF and BSW

Imperial button heads are sized by gauge (#4 to #10) or inch diameter, with a UNC (coarse), UNF (fine) or BSW thread. The alloy steel screws are to ASTM F835 (the 1/2 inch BSW class 12.9 to BS 2470) and the 304 stainless ones to ANSI B18.3.

Imperial button head socket screws, hex socket drive. Lengths in inches under the head. Pack is the minimum order quantity. Tap a number to show it in the selector above.

SizeThreadMaterialLengthsPack
Plain alloy steel, class 12.9
1/2 inchBSWPlain alloy steel, class 12.91", 1-1/4", 1-1/2", 2"50
Plain alloy steel
#4UNCPlain alloy steel1/4", 3/8", 1/2"100
#6UNCPlain alloy steel1/4", 3/8", 1/2"100
#8UNCPlain alloy steel1/4", 3/8", 1/2"100
#10UNCPlain alloy steel1/4", 3/8", 1/2", 5/8", 3/4", 1"100
1/4 inchUNCPlain alloy steel3/8", 1/2", 5/8", 3/4", 1"100
5/16 inchUNCPlain alloy steel3/8", 1/2", 5/8", 3/4", 7/8", 1"100
3/8 inchUNCPlain alloy steel1/2", 5/8", 3/4", 1", 1-1/4", 1-1/2", 2"100
1/2 inchUNCPlain alloy steel1", 1-1/4", 1-1/2", 2", 2-1/2", 3"50
5/8 inchUNCPlain alloy steel1", 1-1/4", 1-1/2", 2", 2-1/2", 3"25
#10UNFPlain alloy steel1/4", 3/8", 1/2", 5/8", 3/4", 1"100
1/4 inchUNFPlain alloy steel3/8", 1/2", 5/8", 3/4", 1"100
5/16 inchUNFPlain alloy steel3/8", 1/2", 5/8", 3/4", 1"100
3/8 inchUNFPlain alloy steel1/2", 3/4", 1", 1-1/4"100
Zinc plated alloy steel
1/4 inchUNCZinc plated alloy steel1/2", 5/8", 3/4", 1"100
5/16 inchUNCZinc plated alloy steel1/2", 5/8", 3/4", 1"100
3/8 inchUNCZinc plated alloy steel3/4", 1", 1-1/4", 1-1/2", 2"100
304 stainless
#6UNC304 stainless1/4", 3/8", 1/2"100
#8UNC304 stainless1/4", 3/8", 1/2", 3/4", 1"100
#10UNC304 stainless3/8", 1/2", 5/8", 3/4", 1", 1-1/4"100
1/4 inchUNC304 stainless3/8", 1/2", 5/8", 3/4", 1", 1-1/4", 1-1/2", 1-3/4", 2"100
5/16 inchUNC304 stainless5/8", 3/4", 1", 1-1/4", 1-1/2", 2"100
3/8 inchUNC304 stainless1"50
#10UNF304 stainless3/8", 1-1/4"100
1/4 inchUNF304 stainless5/8"100
3/8 inchUNF304 stainless1"50
316 stainless
3/8 inchUNC316 stainless3/4", 1", 1-1/4", 1-1/2", 2"50

Button head screw torque

Guide torques from Hobson's SOKO range tightening torque sheet for button head screws in reduced head class 010.9 (alloy steel, metric coarse thread). The sheet covers the Soko range only: our 010.9 button heads are Soko, so it applies to them. Hobson works the figures on a k factor of 0.2 for plain threads with a light oil coating and 0.14 for zinc plated, for the first tightening of a single assembly, with the clamp load worked at 360MPa bolt stress. They are a guide only; critical joints need a proper tension method set by an engineer.

They do not apply to the stainless or zinc flake button heads, or to our zinc plated class 08.8 button heads (M6 and M8), which are Hobson brand, not Soko, and have no torque sheet in the documents we hold. We give no torque for class 012.9 button heads: do not use the cap screw torques on them; use the torque the joint design specifies.

Guide tightening torque in Nm for Soko class 010.9 alloy steel button head screws, from Hobson's SOKO range tightening torque sheet (button head columns). We carry Soko 010.9 in plain M4 to M10 and zinc plated M4 to M12. Not for the Hobson brand 08.8, stainless, zinc flake or 012.9 button heads. Tap a number to show it in the selector above.

Size010.9 plain010.9 zinc plated
M42.51.8
M55.13.6
M68.76.1
M821.114.8
M1041.829.2
M1272.851.0

Alloy steel, zinc or stainless button heads?

  • Plain alloy steel: no coating, supplied lightly oiled, for dry indoor work.
  • Zinc plated: a 5 micron zinc coating for indoor and non-corrosive conditions.
  • Zinc flake silver (class 12.9): a 10 micron coating with high corrosion resistance and no risk of hydrogen embrittlement.
  • 304 and 316 stainless: for outdoor and damp work. Hobson's corrosion guide calls for 316 within 2m of a pool edge, and 316 has better resistance near the sea; neither 304 nor 316 is made to sit in seawater. Lubricate stainless threads, or use a different stainless grade for the nut, to help prevent galling.

Fitting button head screws

  1. Use a hex key or bit that fits the socket fully; a worn key rounds out the small button head socket.
  2. Pick a length that gives full thread engagement in the nut or tapped hole.
  3. Tighten to the button head torque for the class and finish, not a socket head cap screw figure.
  4. Fit a flat washer under the head on soft or slotted material.

Button head screws in Adelaide

Allmat supplies button head screws, socket head cap screws, nuts and washers to fabricators, mechanics, shopfitters and trade across Adelaide and South Australia. Add them to a quote with the rest of your list, and we will price the lot.

Button head screws for the job

Button head socket screws in alloy steel and stainless, with the nuts and washers to go with them, are available to order from Allmat for fabricators, mechanics, shopfitters, builders and trade across Adelaide and South Australia. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.

Send your list for a quoteCall 1300 03 03 63

Goes with

Questions

What is the difference between a button head and a socket head cap screw?

A button head has a low, rounded head; a socket head cap screw has a taller cylinder head. The button head is reduced strength (marked 08.8, 010.9 or 012.9) and takes a lower torque, so use a socket head cap screw where the joint needs full strength.

Are button head bolts as strong as normal bolts?

No. Hobson's Soko guide says button heads have reduced loadability because the head has a smaller stress area than the thread. The thread is the same class but the joint cannot be loaded to the full class.

What drive do button head screws take?

Most take a hex key (Allen key) in a hex socket. The 304 stainless Torx button heads take T40 (M8), T50 (M10) and T55 (M12). Ask us if you need the hex key size for a particular screw.

What torque for an M8 button head screw?

From Hobson's Soko sheets, an M8 Soko 010.9 button head takes 21.1Nm plain or 14.8Nm zinc plated, for the first tightening of a single assembly. These are a guide only and are not for the Hobson brand 08.8, stainless or 012.9 button heads.

Do you have stainless button head screws?

Yes: 304 stainless M3 to M16 with hex socket drive and M8 to M12 with Torx drive, 316 stainless M3 to M12 and 3/8 inch UNC, and 304 imperial UNC and UNF sizes.

What are dome head bolts?

Another name for button head socket screws: a low domed head with a hex or Torx socket.

Where can I buy button head screws in Adelaide?

Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.

Socket Button Screw: sizes and finishes we supply

525 lines by type and finish. Pick one above for its product code and pack sizes.

HeadFinishSizesLengthsLines
Button304 StainlessM3, M4, M5, M6, M8, M10, M12, M164 to 100 (20 lengths)117
ButtonZinc PlatedM4, M5, M6, M8, M10, M12, M166 to 100 (20 lengths)114
ButtonSteelM3, M4, M5, M6, M8, M10, M12, M166 to 70 (14 lengths)90
Button316 StainlessM3, M4, M5, M6, M8, M10, M125 to 70 (15 lengths)69
ButtonSteel1/4, 5/16, 3/8, 1/2, 5/8, #4, #6, #8, #101/4 to 3 inch (12 lengths)69
Button304 Stainless1/4, 5/16, 3/8, #6, #8, #101/4 to 2 inch (10 lengths)34
ButtonZinc Flake SilverM3, M4, M5, M6, M8, M10, M128, 10, 16, 20, 25, 30, 35, 5014
ButtonZinc Plated1/4, 5/16, 3/81/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 2 inch13
Button316 Stainless3/83/4, 1, 1-1/4, 1-1/2, 2 inch5

Data sheets and documents

The documents for the product you choose are listed with the selector above. Here is every Socket Button Screw document from Hobson Engineering.

All Socket Button Screw documents (16)

Need them in bulk?

Add the sizes you need to your quote, or send us your list and we’ll price the lot and supply it with the rest of your order.

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