if your frizzen is 1 inch wide , then you need a 1 inch wide flint .
being 1 1/8 at the half cock then your looking for a 1 to 1 1/8 long flint .
myself i would go the short 1 inch and move the flint out alittle . if you go with the 1 1/8 , you may have to notch out the back of the flint alittle so as to move it back .
really neather size will be a problem as through the life of the flint, your going to be slowly moving it forward anyway