| Clue | Source | Date |
|---|---|---|
| Cover for an exposed bolt end | ||
| Domed top for a threaded fastener | The Washington Post | 25 Apr 2021 |
| Domed top for a threaded fastener | LA Times Daily | 25 Apr 2021 |
| Hemispherical fastener | ||
| Bit of plumbing hardware | ||
| Hemispherical fastener | ||
| Screw backer |