The nipple sizes indicated as "6.1" and "6.75" should read:
"6.1" is 6-1mm
"6.75" is 6 -.75mm
With few exceptions,
American-made rifles use 1/4" X 28; (T/C side lock models for example)
Italian-made rifles use 6-.75mm (Lyman Great Plains Rifle, for example) (Muskets are a whole new ball game)
Spanish-made rifles use 6-1mm (CVA & Traditions imports, for example)