The blade nut on MT5097.1Z sheared off when refitting after sharpening blade, torque setting 65/70NM. Thread is in the shaft. What parts are required if I cannot remove old thread?

We have had a look for you and you would need to buy part number 18 on the below diagram: https://www.lsengineers.co.uk/catalog/product/view/id/180379 However, it maybe better to remove the broken thread by using a screw extraction set - https://www.lsengineers.co.uk/catalog/product/view/id/3147