Earlier versions seem to have been an actual nut shape. Francatelli explains that the dough should be rolled into balls the size of a walnut.
Original Receipt in 'The Art of Cookery Made Easy and Refined' By John Mollard (Mollard 1802)GOOD GINGERBREAD NUTS,
Take four pounds of flour, half a pound of sifted sugar, one ounce of carraway seeds, half an ounce of ginger pounded and sifted, six ounces of fresh butter, and two ounces of candied orenge peel cut into small slices. Then take a pound of treacle or honey and a gill of cream, make them warm together, mix all the ingredients into a paste, and let it lay six hours; then roll it out, shape it into nuts, and bake them in a moderate oven
2014
Ginger Nuts can be very hard indeed - "How a gingerbread biscuit took out the prime minister"...
The Times, 27 June, 1892
During Mr Gladstone's progress through the streets there was a most regrettable occurrence. Baron Halkett, who was in the carriage with Mr Gladstone, states that he saw a woman raise her hand and throw something with great violence towards Mr Gladstone. It struck him in the corner of the left eye and inflicted a slight wound and caused bleeding of the nose.
Mr Gladstone immediately put his hand over his eye and fell back into his carriage and said to Baron Halkett, "It was a cruel thing to do. I hope some notice will be taken of it."
The substance thrown fell upon the knees of Mr James Tomkinson and turned out to be a hard gingerbread nut. (Source: BBC)