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Hex cap screw dimensions (inches)
Width across flats F and head height H are basic dimensions from ASME B18.2.1 Table 6. Across corners G is the minimum value. Threads are Unified coarse (UNC) or fine (UNF), class 2A. The mm column is a straight conversion of F (1 in = 25.4 mm), calculated for buyers who use metric tools.
| Diameter | UNC TPI | UNF TPI | Width across flats F | F in mm (calc.) | Across corners G min | Head height H | Inquiry |
|---|---|---|---|---|---|---|---|
| 1/4 | 20 | 28 | 7/16 | 11.1 | 0.488 | 5/32 | Quote this size |
| 5/16 | 18 | 24 | 1/2 | 12.7 | 0.557 | 13/64 | Quote this size |
| 3/8 | 16 | 24 | 9/16 | 14.3 | 0.628 | 15/64 | Quote this size |
| 7/16 | 14 | 20 | 5/8 | 15.9 | 0.698 | 9/32 | Quote this size |
| 1/2 | 13 | 20 | 3/4 | 19.1 | 0.840 | 5/16 | Quote this size |
| 9/16 | 12 | 18 | 13/16 | 20.6 | 0.910 | 23/64 | Quote this size |
| 5/8 | 11 | 18 | 15/16 | 23.8 | 1.051 | 25/64 | Quote this size |
| 3/4 | 10 | 16 | 1-1/8 | 28.6 | 1.254 | 15/32 | Quote this size |
| 7/8 | 9 | 14 | 1-5/16 | 33.3 | 1.465 | 35/64 | Quote this size |
| 1 | 8 | 12 | 1-1/2 | 38.1 | 1.675 | 39/64 | Quote this size |
| 1-1/8 | 7 | 12 | 1-11/16 | 42.9 | 1.859 | 11/16 | Quote this size |
| 1-1/4 | 7 | 12 | 1-7/8 | 47.6 | 2.066 | 25/32 | Quote this size |
| 1-1/2 | 6 | 12 | 2-1/4 | 57.2 | 2.480 | 15/16 | Quote this size |
Thread length (inches)
ASME B18.2.1 sets a minimum thread length LT that depends on the screw length. For screws 6 in long or shorter, LT is 2D + 1/4 in. For screws longer than 6 in, it is 2D + 1/2 in. Screws too short for that thread length are threaded close to the head.
| Diameter | LT for L ≤ 6 in | LT for L > 6 in | Inquiry |
|---|---|---|---|
| 1/4 | 0.75 | 1.00 | Quote this size |
| 5/16 | 0.875 | 1.125 | Quote this size |
| 3/8 | 1.00 | 1.25 | Quote this size |
| 7/16 | 1.125 | 1.375 | Quote this size |
| 1/2 | 1.25 | 1.50 | Quote this size |
| 5/8 | 1.50 | 1.75 | Quote this size |
| 3/4 | 1.75 | 2.00 | Quote this size |
| 7/8 | 2.00 | 2.25 | Quote this size |
| 1 | 2.25 | 2.50 | Quote this size |
| 1-1/4 | 2.75 | 3.00 | Quote this size |
| 1-1/2 | 3.25 | 3.50 | Quote this size |
SAE J429 grades and head markings
The grade sets the steel, heat treatment and strength. It is shown by radial lines on the head, plus the manufacturer's mark. Values below are from Portland Bolt's published SAE J429 and ASTM summary.
| Grade | Material | Diameter (in) | Proof load (ksi) | Min yield (ksi) | Min tensile (ksi) | Head marking | Inquiry |
|---|---|---|---|---|---|---|---|
| SAE Grade 2 | Low or medium carbon steel | 1/4 – 3/4 | 55 | 57 | 74 | No grade lines | Quote this size |
| SAE Grade 2 | Low or medium carbon steel | 7/8 – 1-1/2 | 33 | 36 | 60 | No grade lines | Quote this size |
| SAE Grade 5 | Medium carbon steel, quenched & tempered | 1/4 – 1 | 85 | 92 | 120 | 3 radial lines (120° apart) | Quote this size |
| SAE Grade 5 | Medium carbon steel, quenched & tempered | 1-1/8 – 1-1/2 | 74 | 81 | 105 | 3 radial lines (120° apart) | Quote this size |
| SAE Grade 8 | Medium carbon alloy steel, quenched & tempered | 1/4 – 1-1/2 | 120 | 130 | 150 | 6 radial lines (60° apart) | Quote this size |
Need these ASME B18.2.1 sizes? Request a quote
- Grade 2 values for 1/4 – 3/4 in apply to headed screws up to 6 in long. Longer screws fall back to the lower Grade 1 values.
- ASTM A449 Type 1 matches Grade 5 strength up to 1-1/2 in and extends to 3 in at lower values (90 ksi tensile for 1-5/8 – 3 in).
- ASTM A307 Grade A is a 60 ksi low-carbon bolt, often specified for general construction.
Matching nuts and their weights
Grade 5 cap screws are normally paired with Grade 5 finished hex nuts and Grade 8 screws with Grade 8 nuts. For heavy structural joints, heavy hex nuts are used. Approximate weights of plain steel nuts from Portland Bolt's nut weight chart are below; use them with your screw weights to plan freight.
| Size | Finished hex nut (lb / 100) | Heavy hex nut (lb / 100) | Inquiry |
|---|---|---|---|
| 1/2 | 3.75 | 6.54 | Quote this size |
| 5/8 | 7.33 | 11.9 | Quote this size |
| 3/4 | 11.9 | 19.3 | Quote this size |
| 7/8 | 19.0 | 29.7 | Quote this size |
| 1 | 28.3 | 42.5 | Quote this size |
Hex cap screw, hex bolt and heavy hex: what is the difference?
ASME B18.2.1 lists several hex-head products. A hex cap screw has a washer face under the head, tighter tolerances and a chamfered point; it is the usual choice for machinery. A hex bolt has looser tolerances and is mainly used with a nut in construction. Heavy hex screws and structural bolts (ASTM F3125 A325 / A490) have larger heads; see our A325 dimension chart for those.
Do not mix inch and metric parts in one assembly. A 1/2-13 screw is 12.7 mm in diameter and will not fit an M12 nut.
Finishes and hydrogen embrittlement
- Plain, zinc plated (clear or yellow) and black oxide are common for Grade 5 and Grade 8.
- Grade 5 can be hot-dip galvanized; nuts must be overtapped to fit.
- Grade 8 should not be hot-dip galvanized because of embrittlement risk. Zinc plating needs baking; zinc flake is a safer choice.
How to specify inch hex cap screws in your RFQ
- Standard: ASME B18.2.1 hex cap screw, heavy hex screw or hex bolt.
- Diameter, threads per inch (UNC or UNF) and length in inches, e.g. 1/2-13 × 2.
- Grade: SAE J429 Grade 2, 5 or 8, ASTM A307, A449, or stainless 18-8 / 316.
- Finish: plain, zinc, yellow zinc, black oxide, hot-dip galvanized (Grade 5 and below) or zinc flake.
- Matching nuts and washers, quantity per size and packaging (boxes, kegs or bulk).
Order these sizes from HEXVARO
Send your size list with grade, finish and quantity — we reply within 2 working hours with price, lead time and shipping terms.
- Reply: within 2 working hours
- MOQ: 500 pcs per specification
- Lead time: 10–15 days stock items
- Payment: T/T · L/C · PayPal
- Shipping ports: Tianjin · Ningbo · Shanghai · Shenzhen
- Incoterms: EXW · FOB · CFR · CIF · DAP
- Experience: Founder with 10+ years in the fastener industry
Frequently asked questions
What wrench size fits a 1/2 inch hex bolt?
A 3/4 inch wrench fits a 1/2-13 hex cap screw. A 3/8 inch screw takes 9/16 inch and a 5/8 inch screw takes 15/16 inch.
What is the difference between Grade 5 and Grade 8?
SAE Grade 5 is medium-carbon steel, quenched and tempered, with 120 ksi minimum tensile up to 1 inch. Grade 8 is medium-carbon alloy steel with 150 ksi minimum tensile. Head markings are 3 and 6 radial lines respectively.
How do I identify a Grade 2 bolt?
SAE Grade 2 has no radial lines on the head. If a head has no grade lines or numbers, treat it as no better than Grade 2.
Can Grade 8 bolts be galvanized?
Hot-dip galvanizing Grade 8 should be avoided because of hydrogen embrittlement risk. Use zinc flake, or zinc plating with baking.
Are inch structural bolts the same as hex cap screws?
No. A325 / A490 structural bolts are heavy hex with a larger head and shorter thread. See the A325 dimension chart.
What is the MOQ for inch hex bolts?
Reference MOQ is 500 pcs per specification. Stock sizes typically ship in 10–15 days and made-to-order sizes in 25–30 days, subject to quotation. We reply to every RFQ within 2 working hours.
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