| THREAD SERIES DESIGNATOR | UNC |
| NOMINAL THREAD DIAMETER | 0.250 INCHES |
| THREAD QUANTITY PER INCH | 20 |
| THREAD CLASS | 2A |
| THREAD DIRECTION | RIGHT-HAND |
| THREAD LENGTH | 0.369 INCHES MINIMUM AND |
| 0.469 INCHES MAXIMUM |
| FASTENER LENGTH | 0.469 INCHES MINIMUM AND |
| 0.500 INCHES MAXIMUM |
| MATERIAL | STEEL COMP 1050 PRIMARY WASHER |
| STEEL FASTENER |
| MATERIAL DOCUMENT AND CLASSIFICATION | SAE ASSN STD SINGLE MATERIAL RESPONSE PRIMARY WASHER |
| 66,1010-1020 FED STD SINGLE MATERIAL RESPONSE FASTENER |
| SURFACE TREATMENT | ZINC PRIMARY WASHER |
| CADMIUM FASTENER |
| SURFACE TREATMENT DOCUMENT AND CLASSIFICATION | QQ-Z-325,TY 1,CL 3 FED SPEC SINGLE TREATMENT RESPONSE PRIMARY WASHER |
| QQ-P-416,TY 1,CL 3 FED SPEC SINGLE TREATMENT RESPONSE FASTENER |
| HEAD STYLE | ROUND |
| HEAD DIAMETER | 0.443 INCHES MINIMUM AND |
| 0.472 INCHES MAXIMUM |
| HEAD HEIGHT | 0.160 INCHES MINIMUM AND |
| 0.175 INCHES MAXIMUM |
| INTERNAL DRIVE STYLE | SLOT |
| WASHER QUANTITY | 1 |
| PRIMARY WASHER STYLE | FLAT EXTERNAL TEETH |
| PRIMARY WASHER OUTSIDE DIAMETER | 0.460 INCHES MINIMUM AND |
| 0.475 INCHES MAXIMUM |
| PRIMARY WASHER MATERIAL THICKNESS | 0.023 INCHES MINIMUM AND |
| 0.028 INCHES MAXIMUM |
| SPEC/STD CONTROLLING DATA | |
| MANUFACTURERS CODE | 21450 |
| DEFINITIVE GOVERNMENT SPEC/STD REFERENCE | 420991 |