| Sg. Indef. | harðjaxl |
| Sg. Def. | harðjaxlinn |
| Pl. Indef. | harðjaxlar |
| Pl. Def. | harðjaxlarnir |
| Sg. Indef. | harðjaxls |
| Sg. Def. | harðjaxlsins |
| Pl. Indef. | harðjaxla |
| Pl. Def. | harðjaxlanna |
| Sg. Indef. | harðjaxli |
| Sg. Def. | harðjaxlinum |
| Pl. Indef. | harðjöxlum |
| Pl. Def. | harðjöxlunum |
| Sg. Indef. | harðjaxl |
| Sg. Def. | harðjaxlinn |
| Pl. Indef. | harðjaxla |
| Pl. Def. | harðjaxlana |