Nipple for an 1861 Enfield

[tokguy]

My grandfather is looking for an precussion cap nipple for an 1861 Enfield. If someone out there knows what size we ought to be looking for or where to find it ; help in restoring this old piece of history would be greatly appriecated.
Thanks Tokguy

 

[Steppenwolf]

5/16-18 thread

Track of the Wolf sells them around $4.00 each.