Material specification page for round head machine screws, unc (slotted and phillips) in Property Class 12.9 Steel. Covers the grade designation (ISO 898-1 property class 12.9), corrosion and magnetic behavior, comparable grades and their trade-offs, and the sizes available to ASME B18.6.3.
Why Choose Property Class 12.9 Steel for Round Head Machine Screws, UNC (Slotted and Phillips)
The highest common strength class, for high-load machine assembly. For round head machine screws, unc (slotted and phillips), this matters when requires plating or black-oxide protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 898-1 property class 12.9 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | commonly limited to approx. +300 °C; confirm against the coating and the load |
| Corrosion characteristic | Requires plating or black-oxide protection |
Corrosion Behavior in Service
Carbon and alloy steel round head machine screws, unc (slotted and phillips) 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 Round Head Machine Screws, UNC (Slotted and Phillips), class 8.8 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 12.9 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 12.9 Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
Grade 12 9 Steel is one of the grades the catalog describes. Head form and drive can be specified to the assembly rather than to a standard: a larger bearing face, a security drive, or a socket sized for the tool already on the bench. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.

