Property Class 8.8 Steel (ISO 898-1 property class 8.8) is the workhorse medium-carbon alloy class for structural joints. When round head machine screws, unc (slotted and phillips) are specified in this grade, the dimensions remain per ASME B18.6.3; the material determines corrosion behavior (requires plating (zinc) for corrosion protection) and the service temperature range (commonly limited to approx. +300 °C; confirm against the coating and the load). Both are covered below with the size table.
Why Choose Property Class 8.8 Steel for Round Head Machine Screws, UNC (Slotted and Phillips)
The workhorse medium-carbon alloy class for structural joints. For round head machine screws, unc (slotted and phillips), 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 |
Galvanic & Galling Considerations
For round head machine screws, unc (slotted and phillips) in steel, the dominant compatibility issue is hydrogen embrittlement at high property classes (10.9 and above) when electroplated. Plating must be followed by an appropriate baking treatment, or a non-electroplated finish (mechanical zinc, zinc flake) should be substituted.
Comparable Grades
For Round Head Machine Screws, UNC (Slotted and Phillips), 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 Round Head Machine Screws, UNC (Slotted and Phillips) Available in Property Class 8.8 Steel
| Size | Type | Pitch P (mm) | Head diameter dk (in) | Head height k (in) | J (in) | T (in) | Length range l (in) | Reference standard |
|---|---|---|---|---|---|---|---|---|
| #0 | Cross recessed round head screws | 0.318 | 0.113 | 0.053 | 0.023 | 0.039 | 1/16"~1 1/2" | ASME B18.6.3 |
| #0 | Slotted round head screws | 0.318 | 0.113 | 0.053 | 0.023 | 0.039 | 1/16"~1 1/2" | ASME B18.6.3 |
| #1 | Cross recessed round head screws | 0.397 | 0.138 | 0.061 | 0.026 | 0.044 | 1/16"~1 1/2" | ASME B18.6.3 |
| #1 | Slotted round head screws | 0.397 | 0.138 | 0.061 | 0.026 | 0.044 | 1/16"~1 1/2" | ASME B18.6.3 |
| #2 | Cross recessed round head screws | 0.454 | 0.162 | 0.069 | 0.031 | 0.048 | 1/16"~2 1/2" | ASME B18.6.3 |
| #2 | Slotted round head screws | 0.454 | 0.162 | 0.069 | 0.031 | 0.048 | 1/16"~2 1/2" | ASME B18.6.3 |
| #3 | Cross recessed round head screws | 0.529 | 0.187 | 0.078 | 0.035 | 0.053 | 1/8"~2 1/2" | ASME B18.6.3 |
| #3 | Slotted round head screws | 0.529 | 0.187 | 0.078 | 0.035 | 0.053 | 1/8"~2 1/2" | ASME B18.6.3 |
| #4 | Cross recessed round head screws | 0.635 | 0.211 | 0.086 | 0.039 | 0.058 | 1/8"~4" | ASME B18.6.3 |
| #4 | Slotted round head screws | 0.635 | 0.211 | 0.086 | 0.039 | 0.058 | 1/8"~4" | ASME B18.6.3 |
| #5 | Cross recessed round head screws | 0.635 | 0.236 | 0.095 | 0.043 | 0.063 | 3/16"~4" | ASME B18.6.3 |
| #5 | Slotted round head screws | 0.635 | 0.236 | 0.095 | 0.043 | 0.063 | 3/16"~4" | ASME B18.6.3 |
| #6 | Cross recessed round head screws | 0.794 | 0.26 | 0.103 | 0.048 | 0.068 | 1/8"~4" | ASME B18.6.3 |
| #6 | Slotted round head screws | 0.794 | 0.26 | 0.103 | 0.048 | 0.068 | 1/8"~4" | ASME B18.6.3 |
| #8 | Cross recessed round head screws | 0.794 | 0.309 | 0.120 | 0.054 | 0.077 | 1/8"~5" | ASME B18.6.3 |
| #8 | Slotted round head screws | 0.794 | 0.309 | 0.120 | 0.054 | 0.077 | 1/8"~5" | ASME B18.6.3 |
| #10 | Cross recessed round head screws | 1.058 | 0.359 | 0.137 | 0.06 | 0.087 | 3/16"~8" | ASME B18.6.3 |
| #10 | Slotted round head screws | 1.058 | 0.359 | 0.137 | 0.06 | 0.087 | 3/16"~8" | ASME B18.6.3 |
| #12 | Cross recessed round head screws | 1.058 | 0.408 | 0.153 | 0.067 | 0.096 | 1/4"~8" | ASME B18.6.3 |
| #12 | Slotted round head screws | 1.058 | 0.408 | 0.153 | 0.067 | 0.096 | 1/4"~8" | ASME B18.6.3 |
| 1/4" | Cross recessed round head screws | 1.27 | 0.472 | 0.175 | 0.075 | 0.109 | 3/8"~10" | ASME B18.6.3 |
| 1/4" | Slotted round head screws | 1.27 | 0.472 | 0.175 | 0.075 | 0.109 | 3/8"~10" | ASME B18.6.3 |
| 5/16" | Cross recessed round head screws | 1.411 | 0.59 | 0.216 | 0.084 | 0.132 | 1/2"~10" | ASME B18.6.3 |
| 5/16" | Slotted round head screws | 1.411 | 0.59 | 0.216 | 0.084 | 0.132 | 1/2"~10" | ASME B18.6.3 |
| 3/8" | Cross recessed round head screws | 1.587 | 0.708 | 0.256 | 0.094 | 0.155 | 1/2"~12" | ASME B18.6.3 |
| 3/8" | Slotted round head screws | 1.587 | 0.708 | 0.256 | 0.094 | 0.155 | 1/2"~12" | ASME B18.6.3 |
| 7/16" | Cross recessed round head screws | 1.814 | 0.75 | 0.328 | 0.094 | 0.196 | 3/4"~12" | ASME B18.6.3 |
| 7/16" | Slotted round head screws | 1.814 | 0.75 | 0.328 | 0.094 | 0.196 | 3/4"~12" | ASME B18.6.3 |
| 1/2" | Cross recessed round head screws | 1.954 | 0.813 | 0.355 | 0.106 | 0.211 | 3/4"~12" | ASME B18.6.3 |
| 1/2" | Slotted round head screws | 1.954 | 0.813 | 0.355 | 0.106 | 0.211 | 3/4"~12" | ASME B18.6.3 |
Dimensions are independent of the material: every size above is available in Property Class 8.8 Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
Grade 8 8 Steel is one of the grades the catalog describes. Where the standard stops, the drawing takes over: fine pitches, left-hand threads, partial threading, and property classes above the catalogued grade where material and heat treatment allow. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.

