Chrome hob caps that screw into the nuts that hold the top (hob) in place.
These chrome buttons fit all Rayburn 2 oven models. Please note these are size 24mm diameter with a 3/8 inch threaded stud and are NOT the same as the smaller Aga deluxe ones. See here for these.
Being soft chrome these nuts are often damage during removal and need replacing. If set solid by years of cooking grime the easiest method of removal is to cut a small notch on one side and then tap with a screwdriver to undo.