Hex Head Cap Screws, UNC manufactured in Property Class 8.8 Steel (ISO 898-1 property class 8.8) are dimensioned to ASME B18.2.1. The sections below give the mechanical and physical properties of the grade, its behavior in corrosive and elevated-temperature service, and the full size table.
Why Choose Property Class 8.8 Steel for Hex Head Cap Screws, UNC
The workhorse medium-carbon alloy class for structural joints. For hex head cap screws, unc, this matters when requires plating (zinc) for corrosion protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 898-1 property class 8.8 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | commonly limited to approx. +300 °C; confirm against the coating and the load |
| Corrosion characteristic | Requires plating (zinc) for corrosion protection |
Corrosion Behavior in Service
Carbon and alloy steel hex head cap screws, unc require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.
Comparable Grades
For Hex Head Cap Screws, UNC, class 10.9 or 12.9 is the comparable strength step. Move up when the joint preload approaches the proof load of the current class; move down when the joint is over-specified. For corrosion-critical service, switch to stainless A2 or A4.
Sizes of Hex Head Cap Screws, UNC Available in Property Class 8.8 Steel
| Size | b (mm) | Pitch P (mm) | c (mm) | dw (mm) | Width across corners e (mm) | Head height k (mm) | r (mm) | Width across flats s (mm) | Length range l (in) | Reference standard |
|---|---|---|---|---|---|---|---|---|---|---|
| 1/4" | 19.05 | 1.27 | 0.406 | 10.557 | 12.832 | 4.366 | 0.37 | 11.113 | 3/8"~12" | ASME B18.2.1 |
| 5/16" | 22.225 | 1.411 | 0.406 | 12.065 | 14.665 | 5.556 | 0.423 | 12.7 | 1/2"~12" | ASME B18.2.1 |
| 3/8" | 25.4 | 1.587 | 0.406 | 13.573 | 16.498 | 6.35 | 0.476 | 14.287 | 1/2"~12" | ASME B18.2.1 |
| 7/16" | 28.575 | 1.814 | 0.406 | 15.081 | 18.331 | 7.541 | 0.529 | 15.875 | 3/4"~12" | ASME B18.2.1 |
| 1/2" | 31.75 | 1.954 | 0.406 | 18.098 | 21.997 | 8.731 | 0.635 | 19.05 | 3/4"~12" | ASME B18.2.1 |
| 5/8" | 38.1 | 2.309 | 0.406 | 22.622 | 27.496 | 10.716 | 0.794 | 23.812 | 3/4"~14" | ASME B18.2.1 |
| 3/4" | 44.45 | 2.54 | 0.406 | 27.146 | 32.996 | 12.7 | 0.953 | 28.575 | 1"~14" | ASME B18.2.1 |
| 7/8" | 50.8 | 2.822 | 0.406 | 31.671 | 38.495 | 14.684 | 1.111 | 33.337 | 1 1/2"~14" | ASME B18.2.1 |
| 1" | 57.15 | 3.175 | 0.406 | 36.195 | 43.994 | 17.066 | 1.27 | 38.1 | 1 1/2"~14" | ASME B18.2.1 |
| 1 1/8" | 63.5 | 3.629 | 0.406 | 40.719 | 49.493 | 19.05 | 1.429 | 42.862 | 1 5/8"~14" | ASME B18.2.1 |
| 1 1/4" | 69.85 | 3.629 | 0.406 | 45.244 | 54.993 | 21.431 | 1.587 | 47.625 | 1 5/8"~14" | ASME B18.2.1 |
| 1 3/8" | 76.2 | 4.233 | 0.406 | 49.768 | 60.492 | 23.019 | 1.746 | 52.388 | 1 3/4"~14" | ASME B18.2.1 |
| 1 1/2" | 82.55 | 4.233 | 0.406 | 54.292 | 65.991 | 25.4 | 1.905 | 57.15 | 1 3/4"~14" | ASME B18.2.1 |
| 1 3/4" | 95.25 | 5.08 | 0.406 | 63.341 | 76.99 | 29.369 | 2.223 | 66.675 | 2"~14" | ASME B18.2.1 |
| 2" | 107.95 | 5.644 | 0.406 | 72.39 | 87.988 | 34.131 | 2.54 | 76.2 | 2 1/2"~14" | ASME B18.2.1 |
| 2 1/4" | 120.65 | 5.644 | 0.406 | 81.439 | 98.987 | 38.1 | 2.857 | 85.725 | 2 1/2"~14" | ASME B18.2.1 |
| 2 1/2" | 133.35 | 6.35 | 0.406 | 90.487 | 109.985 | 42.069 | 3.175 | 95.25 | 3"~14" | ASME B18.2.1 |
| 2 3/4" | 146.05 | 6.35 | 0.406 | 99.536 | 120.984 | 46.038 | 3.493 | 104.775 | 3"~14" | ASME B18.2.1 |
| 3" | 158.75 | 6.35 | 0.406 | 108.585 | 131.982 | 50.8 | 3.81 | 114.3 | 3 1/2"~14" | ASME B18.2.1 |
| 3 1/4" | 171.45 | 6.35 | 0.406 | 117.634 | 142.981 | 55.562 | 4.128 | 123.825 | 3 3/4"~14" | ASME B18.2.1 |
| 3 1/2" | 184.15 | 6.35 | 0.406 | 126.683 | 153.979 | 58.737 | 4.445 | 133.35 | 3 3/4"~14" | ASME B18.2.1 |
| 3 3/4" | 196.85 | 6.35 | 0.406 | 135.731 | 164.978 | 63.5 | 4.763 | 142.875 | 4"~14" | ASME B18.2.1 |
| 4" | 209.55 | 6.35 | 0.406 | 144.78 | 175.976 | 68.263 | 5.08 | 152.4 | 4"~14" | ASME B18.2.1 |
Dimensions are independent of the material: every size above is available in Property Class 8.8 Steel.
Custom manufacturing · Made to drawing
Need this bolt in a grade that is not listed?
Grade 8 8 Steel is one of the grades the catalog describes. Material and finish are usually what drives a special — a grade the standard part is not stocked in, or a coating chosen against a salt-spray figure instead of a default. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
