'Rmasters3' - Some brief explanation:

The various U.S. Krag rifle and carbine models are basically referred to as model 1892, model 1896, model 1898, and model 1899. (BTW - This is not dependent on the year they were actually manufactured).

Coincidentally, the various models of Krag rear-sights, (rifle and carbine), are also referred to by model 1892, model 1896, model 1898, model 1901, and model 1902. (The "sight model" does not change the model of rifle or carbine the sight is found on).

Many Krag rifles and carbines received 'sight updates'.

For example, it is not unusual to find a model 1896 Krag rifle with a model 1902 rear-sight (and appropriate hand-guard), on it. Such a rifle is still a model 1896 rifle.

"Legitimate" Model 1898 Krag rifles have been found with model 1896, 1898, 1901, or 1902 rear-sights on them.

It appears your Model 1898 Krag rifle is wearing the hand-guard that was used with both the model 1898 and model 1902 rear-sights.

My 'hunch' is that you likely have a model 1902 sight.
A well focused picture, smaller than 768 KB, will allow positive identification.

FWIW - A model 1902 rear-sight "Slide" will work on both a model 1898 and model 1902 rear sight "Leaf". The 1898 sight "Leaf" has smooth edges. The 1902 sight "Leaf" is serrated on its left side.

'Granpas-gun parts' or S&S Firearms will likely have compatible parts for your sight