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SEC 01 / SHCS

A574 socket head cap screws at 180 ksi, and 18-8 stainless button and flat heads where the load is light.

As a socket head cap screws supplier we stock two families and no more: alloy steel A574 in thermal black oxide for fixtures, die sets and counterbored machine joints, and 18-8 stainless button and flat heads for guards, covers and washdown. #4 to 1 in inch, M3 to M24 metric. Sold by the box of 100, dropping to 50 above 1/2 in.

Box of 100 Go / no-go checked Pickup from Austin
180 ksi min, A574 to 1/2 in
M24 Largest metric stocked
LINE 01 / A574 black oxideThree lengths, one diameter
Black-oxide alloy socket head cap screws in three lengths
Thermal black oxide with a light oil film. It is a conversion coating, not a barrier: indoors it is fine, outdoors it rusts.
Line 01 / Alloy steel

Alloy socket head cap screws, black oxide

ASTM A574 alloy steel, quenched and tempered, 180 ksi minimum tensile through 1/2 in and 170 ksi above it. That is higher than a Grade 8 hex cap screw, which is why it ends up in die sets, jig plates and anywhere the head has to live in a counterbore. Heads are knurled and carry the maker's identifier. There is no radial-line system on socket screws, so the alloy is read from the head mark plus the black finish, and we keep them in their own drawers for that reason.

The hex socket is the weak point, not the screw. A 3/8-16 takes a 5/16 in key, and a worn or ball-end key in a 180 ksi socket will round it out before the screw yields. Use a hex bit socket on anything over 1/2 in and keep the ball end for reaching, not for torquing.

Lengths run 1/4 in through 6 in in inch sizes and 8 mm through 120 mm in metric. Thread is UNC on inch unless you ask for UNF, and coarse on metric unless you ask for fine. Partial thread starts at 1 in of grip on most diameters, so if your joint needs full thread to the head, say so on the list and we will confirm which lengths come that way.

Spec
ASTM A574 alloy steel
Tensile
180 ksi to 1/2 in, 170 ksi above
Sizes
#4 to 1 in, M3 to M24
Finish
Thermal black oxide with oil
Basis
Per box of 100, 50 above 1/2 in

Price is quoted against your list and confirmed in writing. Nothing on this page is a binding figure.

Send a parts list Build the designation
LINE 02 / 18-8 stainlessButton and 82° flat
Stainless button head and flat head socket screws in two rows
Button heads sit proud and wide, flat heads disappear into an 82 degree countersink. Neither is a substitute for a cap screw in a load path.
Line 02 / 18-8 stainless

Stainless button and flat head socket screws

18-8 austenitic stainless, #6 to 1/2 in and M4 to M12, in low-profile button heads and 82 degree flat heads. These are the stainless steel fasteners Austin TX shops reach for on guards, enclosures, trim panels and anything that gets hosed down. Tensile is around 70 ksi cold-worked, roughly half a Grade 8, so they hold panels rather than loads.

18-8 galls if you run it dry and fast. A dab of anti-seize costs less than a seized nut, and stainless-into-stainless is the worst case: the thread cold-welds partway in and the screw snaps when you try to back it out. Slow the driver down, and use nickel or copper anti-seize from assembly consumables. Flat heads are the other trap. The 82 degree angle has to match your countersink; a 90 degree countersink leaves the head rim bearing on one line and it will pull through sheet.

Every stainless line here states its alloy. If a list says "stainless cap screws" with nothing after it, our reply asks which alloy before it quotes. Unmarked stainless is not stocked, same rule as unmarked hex. For salt air or pool chemistry we move you to 316, which we carry in hex rather than socket.

Alloy
18-8 austenitic stainless
Tensile
About 70 ksi cold-worked
Heads
Low-profile button, 82° flat
Sizes
#6 to 1/2 in, M4 to M12
Basis
Per box of 100

Below a box quantity we will tell you where to buy five of them instead. That is not the business this counter is in.

Send a parts list

Head size and hex key by diameter

Inch sizes, nominal
Socket head cap screws: head diameter, head height and hex key across flats
ThreadHead diaHead heightHex keyCounterbore dia
#10-240.312 in0.190 in5/32 in3/8 in
1/4-200.375 in0.250 in3/16 in7/16 in
5/16-180.469 in0.312 in1/4 in17/32 in
3/8-160.562 in0.375 in5/16 in5/8 in
7/16-140.656 in0.438 in3/8 in23/32 in
1/2-130.750 in0.500 in3/8 in13/16 in
5/8-110.938 in0.625 in1/2 in1 in
3/4-101.125 in0.750 in5/8 in1-3/16 in
1-81.500 in1.000 in3/4 in1-9/16 in

Head height equals nominal diameter on standard cap screws, which is the quick check when you are sizing a counterbore depth. Button and flat heads are shorter and are not in this table; ask and we will send the figure for the size you need.

Use a hex bit socket over 1/2 in. A rounded socket turns a 180 ksi screw into a drilling job.

What the counter asks before it quotes socket screws

Four fields
01

Thread and pitch

3/8-16 or 3/8-24. On metric, M10 coarse is 1.5 mm pitch and the fine is 1.25 mm. If you only have the screw, bring it and we will gauge it at the counter.

02

Grip, not guess

Length is measured under the head to the tip. Thread engagement wants at least 1× diameter in steel and 2× in aluminum, so tell us what it threads into.

03

Head style

Standard cap, low head, button or 82 degree flat. Low heads take a smaller key and less torque, so do not swap one in to clear an obstruction without checking.

04

Where it lives

Indoors, outdoors, washdown or heat. Black oxide alloy outdoors is a rust complaint in three weeks, and we will say so in the reply rather than ship it quietly.

Who this section is not for

If you want four screws to finish a bracket today, buy them at a hardware store. We quote by the box of 100 because that is how they come off the pallet, and splitting a box costs more counter time than the screws are worth. Full boxes, cut blanks and B7 sets are the business.

We also do not carry Grade 12.9 socket screws under a different label and call them A574. If your drawing calls out 12.9, say so: it is the metric class with roughly the same strength band, and the reply will tell you which of the two we actually have in that size.

Related sections

Socket screws rarely go out alone. Most lists pair them with washers, a thread insert for a stripped hole, or a dowel pin to locate the part before the screws take the load.

Hex cap screws Nuts and washers Thread inserts Dowel pins
FORM / Socket screwsWritten reply, no sales call

Send the thread, length, head style and count

Leave a phone or an email. We need one way to reply.

Thread, length, head style, material, finish, count.

We reply in writing with what is on the shelf and what is not.

LOC / CounterPickup point
46 Market Street, Büro 5
Austin, Texas 82389
United States

Every bag leaves labelled with thread, length, grade, finish, count and lot. How an inquiry moves.