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SEC 02 / HEX

Count the lines on the head: three is Grade 5 at 120 ksi, six is Grade 8 at 150 ksi.

Grade 8 hex cap screws in Austin go out of here in yellow zinc, Grade 5 in clear zinc, 1/4 in through 1 in, UNC as standard and UNF on request. Both carry their SAE J429 head marking. If a head has no lines, we did not sell it to you.

Box of 50 or 100 Head marks on every piece Pickup or freight
150 ksi min, Grade 8
120 ksi min, Grade 5 to 1 in
LINE 03 / Grade 5Three radial lines, clear zinc
Clear zinc Grade 5 hex cap screws showing three radial lines on the heads
Three lines at 120 degrees around the head, plus the maker's mark. Count them before the screw goes in, not after it fails.
Line 03 / SAE J429 Grade 5

Grade 5 hex cap screws, clear zinc

Medium carbon steel, quenched and tempered, 120 ksi minimum tensile through 1 in and 105 ksi above that. This is the grade most equipment is actually built with: guards, gearbox mounts, frame joints, pillow blocks, conveyor stands. Clear zinc gives it a few years indoors or under a cover and stops the bin from staining.

Sizes 1/4-20 through 1-8 UNC with lengths from 1/2 in to 8 in; fine thread in 1/4-28 up to 3/4-16 on request. Thread length follows the standard: twice the diameter plus 1/4 in on screws up to 6 in long, so a 1/2-13 × 3 in has 1-1/4 in of thread and the rest is shank. If your joint needs thread the whole way, that is a tap bolt and it is a different line on the shelf. Ask.

Pair Grade 5 screws with Grade 5 nuts. Dropping a Grade 2 nut onto a Grade 5 screw moves the failure into the nut threads, which strip quietly under load and leave the joint feeling tight. The matching table lives on nuts and washers.

Spec
SAE J429 Grade 5
Head mark
Three radial lines plus maker
Tensile
120 ksi to 1 in, 105 ksi above
Sizes
1/4 to 1 in, UNC and UNF
Finish
Clear zinc
Basis
Per box of 50 or 100 by diameter

Boxes of 100 through 3/8 in, 50 from 7/16 in to 3/4 in, and 25 at 7/8 and 1 in. The reply states the count before you commit.

Send a parts list Build the designation
LINE 04 / Grade 8Six radial lines, yellow zinc
Yellow zinc Grade 8 hex cap screws with six radial lines on the heads
Zinc on a Grade 8 screw is yellow for a reason: so nobody mistakes it for a Grade 5 at arm's length on a dark frame.
Line 04 / SAE J429 Grade 8

Grade 8 hex cap screws, yellow zinc

Medium carbon alloy steel, quenched and tempered to 150 ksi minimum across the whole size range, 1/4 in to 1 in. Six radial lines on the head. Trailer suspension, press frames, hitch plates, anything where the clamp load is doing the work and a Grade 5 is already at its limit. Plain finish is available on request if the joint is getting painted or lives in oil.

The embrittlement note. Electroplating a screw this hard drives hydrogen into the steel, and if it is not baked out the screw can crack under sustained load days or weeks later, with no warning and no visible deformation. Plated Grade 8 is baked after plating by the maker. What that means for you: do not strip and replate Grade 8 in the shop, do not send it to a plater who will not bake it, and do not hot-dip galvanise it. If you need corrosion resistance above what yellow zinc gives, we will talk about 316 or a coated alternative instead of replating.

Grade 8 wants a Grade 8 nut and a through-hardened flat washer. A standard SAE washer under a Grade 8 head dishes at full torque and the joint loses preload. Yellow zinc screws and zinc Grade 8 nuts also need the same finish on both parts, or the galvanic pair starts working on whichever one is bare.

Spec
SAE J429 Grade 8
Head mark
Six radial lines plus maker
Tensile
150 ksi minimum
Sizes
1/4 to 1 in UNC, UNF on request
Finish
Yellow zinc, plain on request
Basis
Per box of 50 or 100 by diameter

Ask before you put plain-finish alloy outdoors. It will show surface rust in the first week of Texas humidity.

Send a parts list

Wrench size and proof load by diameter

UNC, dry threads
Hex cap screws: wrench across flats, thread length and proof load
ThreadWrenchThread length to 6 inGr 5 proof loadGr 8 proof load
1/4-207/16 in3/4 in2,700 lb3,800 lb
5/16-181/2 in7/8 in4,450 lb6,300 lb
3/8-169/16 in1 in6,600 lb9,300 lb
7/16-145/8 in1-1/8 in9,050 lb12,750 lb
1/2-133/4 in1-1/4 in12,050 lb17,000 lb
5/8-1115/16 in1-1/2 in19,200 lb27,100 lb
3/4-101-1/8 in1-3/4 in28,400 lb40,100 lb
7/8-91-5/16 in2 in39,250 lb55,450 lb
1-81-1/2 in2-1/4 in51,500 lb72,700 lb

Proof load is the figure from the SAE J429 tables for the stress area of a UNC thread, and it is what the screw must take without permanent stretch. It is not a torque spec. Torque depends on your lubricant, your washer and your joint, and we do not hand out torque numbers for someone else's assembly.

Grade 8 means six radial lines on the head. If there are no lines, we did not sell it to you.

Four things that go wrong with graded hex

Seen at the counter
01

The coffee can bolt

A replacement pulled from a mixed can, no marks, into a Grade 8 joint. It stretches on the first hard cycle and nobody can say what it was. This is why we do not stock unmarked hex.

02

Stainless as an upgrade

18-8 is about 70 ksi, less than half a Grade 8. Swapping stainless in to stop rust is a strength downgrade and the reply will say so.

03

Soft washer under a hard head

A standard SAE flat washer dishes under Grade 8 preload. Use the through-hardened flat from the washer line.

04

Thread into the shank

A 1/2-13 × 3 in has 1-1/4 in of thread. Pick the length so threads, not shank, land in the nut, or the joint never reaches preload.

Who this section is not for

Structural steel bolting is not this counter. A325 and F3125 heavy hex structural bolts with their own washers and tension control belong with a structural supplier who can hand over the paperwork that goes with them. We carry machine-grade hex, and for flange work we carry B7 studs with 2H nuts instead.

We also make no certification claims. The label on your bag carries the thread, length, grade, finish, count and the lot as received. If your job needs mill certs traced to a heat number, say that in the inquiry and we will tell you plainly whether we can meet it before you order.

Related sections

A hex screw list almost always carries nuts, washers and something to keep them where you put them.

Nuts and washers Socket cap screws Rod and B7 studs Threadlocker
FORM / Graded hexWritten reply, no sales call

Send the thread, length, grade and count

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

Thread, length, grade, finish, count. Say UNF if you need fine thread.

No price here is binding. The written reply is the quote.

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

Plated Grade 8 is baked after plating to drive hydrogen out. Do not replate it in the shop, and do not hot-dip galvanise it.