ASTM F835 – Mechanical & Material Properties
ASTM F835 is the standard specification for quenched and tempered alloy steel socket button head (SBHCS) and flat countersunk head (SFHCS) cap screws. These fasteners are engineered for high-strength, shear-type applications where space is limited and a low-profile head is required. The specification covers nominal thread sizes ranging from 0.060" through 0.625" for button heads and up to 1.5" for flat countersunk heads. Fasteners produced under ASTM F835 must meet rigorous tensile requirements, typically ranging from 122 to 150 ksi, depending on size and head configuration. Because the head geometry is a "critical configuration," full-size tensile loads are calculated at 80% of the minimum heat-treated material strength to account for the recessed socket. To ensure structural integrity, the specification mandates strict controls on decarburization limits, surface discontinuities (per ASTM F788), and hardness (37–44 HRC).
Mechanical Properties
Mechanical acceptance is primarily determined by full-size tensile testing. Screws with a length equal to or greater than 3 diameters must meet the minimum ultimate tensile loads specified in the second table below. For screws where full-size testing is impractical due to length or equipment capacity, machined test specimens may be used as an alternative for sizes larger than 0.500".
| Mechanical Requirements | |||||||
|---|---|---|---|---|---|---|---|
| Screw Size | Full-size Screw | Machined Test Specimen | Hardness | ||||
| Tensile Strength, (min) ksi | Yield Strength at 0.2% Offset, (min) ksi | Tensile Strength, (min) ksi | Elongation (min) 4D | Reduction Area (min) | Rockwell (HRC) | Vickers (DPH) | |
| ≤ 0.5 in | 145 | - | - | - | - | 39 – 44 | 382 – 434 |
| > 0.5 in | 135 | 153 | 170 | 8% | 35% | 37 – 44 | 363 – 434 |
| Minimum Ultimate Tensile Load for Button and Countersunk Head Screws | |||||
|---|---|---|---|---|---|
| Screw Size | Stress Area (in²) | Tensile Load, min (lbf) | |||
| Coarse | Fine | Coarse | Fine | Coarse | Fine |
| - | #0-80 | - | 0.00180 | - | 260 |
| #1-64 | #1-72 | 0.00263 | 0.00278 | 380 | 400 |
| #2-56 | #2-64 | 0.00370 | 0.00394 | 540 | 570 |
| #3-48 | #3-56 | 0.00487 | 0.00523 | 710 | 760 |
| #4-40 | #4-48 | 0.00604 | 0.00661 | 880 | 960 |
| #5-40 | #5-44 | 0.00796 | 0.00830 | 1150 | 1200 |
| #6-32 | #6-40 | 0.00909 | 0.01015 | 1320 | 1470 |
| #8-32 | #8-36 | 0.01400 | 0.01474 | 2030 | 2140 |
| #10-24 | #10-32 | 0.01750 | 0.02000 | 2540 | 2900 |
| 1/4-20 | 1/4-28 | 0.03180 | 0.03840 | 4610 | 5275 |
| 5/16-18 | 5/16-24 | 0.05240 | 0.05800 | 7600 | 8450 |
| 3/8-16 | 3/8-24 | 0.07750 | 0.08780 | 11200 | 12700 |
| 7/16-14 | 7/16-20 | 0.10630 | 0.11870 | 15400 | 17000 |
| 1/2-13 | 1/2-20 | 0.14190 | 0.15990 | 20600 | 23200 |
| 5/8-11 | 5/8-18 | 0.22600 | 0.25800 | 30500 | 34500 |
| 3/4-10 | 3/4-16 | 0.33400 | 0.37300 | 45100 | 50700 |
| 7/8-9 | 7/8-14 | 0.46200 | 0.50900 | 62400 | 69200 |
| 1-8 | 1-12 | 0.60600 | 0.66300 | 81800 | 90400 |
| 1-1/8-7 | 1-1/8-12 | 0.76300 | 0.85800 | 103000 | 116400 |
| 1-1/4-7 | 1-1/4-12 | 0.96900 | 1.07300 | 131000 | 146000 |
| 1-3/8-6 | 1-3/8-12 | 1.15500 | 1.31500 | 156000 | 179000 |
| 1-1/2-6 | 1-1/2-12 | 1.40500 | 1.58100 | 190000 | 215000 |
Material Properties
ASTM F835 screws are fabricated from alloy steel made to fine-grain practice. Threads for diameters through 0.625" must be rolled to ensure fatigue resistance, while larger diameters or lengths may be rolled, cut, or ground. All fasteners must be quenched in oil from above the transformation temperature and tempered at a minimum of 650°F (343°C) to achieve the required hardness and ductility.
| Chemical Requirements | |||||
|---|---|---|---|---|---|
| Carbon (range), % | Phosphorus (max), % | Sulfur (max), % | |||
| Heat Analysis | Product Analysis | Heat Analysis | Product Analysis | Heat Analysis | Product Analysis |
| 0.30 – 0.48 | 0.28 – 0.50 | 0.035 | 0.040 | 0.040 | 0.045 |
Metallurgical Properties
Decarburization is a critical factor for alloy steel screws. ASTM F835 specifies that there shall be no evidence of gross decarburization on the surface. Partial decarburization depth is strictly limited based on the thread pitch (Threads per Inch) to ensure the thread remains hard enough to prevent stripping or fatigue failure.
| Decarburization Limits | |||
|---|---|---|---|
| Threads per Inch | Thread Height, hs | 0.75 hs from Root to Crest, min | 0.1 hs at Root, max |
| 48 | 0.013 | 0.010 | 0.001 |
| 44 | 0.014 | 0.011 | 0.001 |
| 40 | 0.015 | 0.011 | 0.002 |
| 36 | 0.017 | 0.013 | 0.002 |
| 32 | 0.019 | 0.014 | 0.002 |
| 28 | 0.022 | 0.017 | 0.002 |
| 24 | 0.026 | 0.020 | 0.003 |
| 20 | 0.031 | 0.023 | 0.003 |
| 18 | 0.034 | 0.026 | 0.003 |
| 16 | 0.038 | 0.029 | 0.004 |
| 14 | 0.044 | 0.033 | 0.004 |
| 13 | 0.047 | 0.035 | 0.005 |
| 12 | 0.051 | 0.038 | 0.005 |
| 11 | 0.056 | 0.042 | 0.006 |
| 10 | 0.061 | 0.046 | 0.006 |
| 9 | 0.068 | 0.051 | 0.007 |
| 8 | 0.077 | 0.058 | 0.008 |
| 7 | 0.088 | 0.066 | 0.009 |
| 6 | 0.102 | 0.077 | 0.010 |