They state musket caps in the part description and you can see the larger section that fits the caps in the pictures.
What gun do you want the nipple for?
"
Nipple, 6-.75mm metric thread, for Lyman Great Plains Rifle, Trade Rifle & InvestArm rifles,
musket cap, stainless steel, requires a well centered hammer cup!
- Cone length: 0.440"
- Thread journal length: 0.195"
- Overall length: 0.635"
- Diameter of base: 0.307"
Nipple, 6-1mm metric thread, for CVA rifles and shotguns, Traditions, Jukar, and other Spanish mfg. guns,
musket cap, stainless steel, requires a well centered hammer cup!
- Cone length: 0.440"
- Thread journal length: 0.195"
- Overall length: 0.635"
- Diameter of base: 0.307"
Nipple, 1/4-28 thread for rifle, with cone for military musket cap, hardened steel, requires NW-100 musket nipple wrench
- Cone length: 0.440"
- Thread journal length: 0.195"
- Overall length: 0.635"
- Diameter of base: 0.307"