| Year | 1939 |
| Date | 10-Aug |
| Volume | 81 |
| Issue | 1,996 |
| Page | 176 |
| Category | Workshop |
| Part | |
| Title | Lapping |
| Author | O.Usmar |
| Notes | A Process of Controlled Wear Productive of High Finish. External lap, internal expandable lap, heart-breaking, successful lapping, flat lap, use of the lathe, comparison of surface after wear |