Machine Screw vs. Hex Bolt
The line is mostly about size and convention, but there are practical differences in how each is specified and driven.
| Feature | Machine Screw | Hex Bolt |
|---|---|---|
| Typical size range | Under 1/4 in. / M6 | 1/4 in. / M6 and larger |
| Threading | Fully threaded | Often partially threaded |
| Drive | Screwdriver or hex key | Wrench or socket |
| Strength grades | Rarely grade-marked | Grade 2 / 5 / 8 marked |
| Best for | Small precision assembly | Structural and heavy joints |
Verdict
For small tapped-hole assembly, use a machine screw. For anything 1/4 in. or larger under real load, specify a hex bolt and match the grade to the application.