FWIW - A bit of 'lubrication' will normally avoid any scratching of the barrel finish by the Kragcarbine front-sight protector.
Most Shooters will probably prefer having the 'protector' off.
Approximate U.S. Krag front-sight blade heights (blade only, not including fixed base):
rear - M1896 rifle sight - .286" blade
rear - M1896 carbine sight - .266" blade
rear - M1898/1901/1902 rifle sight - .413" blade
rear - M1898/1901/1902 carbine sight - .355" blade
Note: The .355" carbine blade is normally marked with a "C", visible on Right-Side. The .266" carbine blade, used with the M1896 carbine rear-sight, is normally marked low, on Left-Side with a "C", this tends to be hidden by the 'fixed' base.
Attached photograph shows .355" carbine blade and .413" rifle blade.
Attachment 94379