[Doc Hoy]

1/4 means 1/4 inch is the diameter of the threaded part of the nipple. 28 means 28 threads per inch and UNF stands for Unified National Fine which in this case is redundant because for a 1/4 fastener, (or in this case your nipple) 28 threads per inch already is Unified National Fine. Unified National Standard (UNS) for that diameter is 24 threads per inch. Unified National Course (UNC) is 20 threads per inch.

I think the nipple will be okay for two reasons. 1) Nipples of that size will fit in your pistol. 2) The cone size should not matter on that particular pistol unless there is something special about the flame shape that is produced by the original nipple in comparison with the shorter cone. I stopped shooting single shot stuff a while ago but I never encountered a weapon that was overly particular in it's ignition characteristics.

I would try the caps you are using on both the original nipples and on the replacement nipples. If the shorter cone requires a different size cap, you will want to know that before you change out the nipples and then go shooting with the wrong caps.

Always more comforting to have the original parts but in this case, I think you are okay.

Every time the word nipple is typed on this forum I always find a way to drag my own personal preference into the conversation. Most everyone is sick of reading this but here goes.

I personally think you should take the orignial nipples out of the pistol before you shoot it. Schmootz the threads up with some kind of lubricant (Bore lube is okay) and then put the nipple back into the pistol just a little tighter than snug but not too tight. Then when you clean the pistol, clean it with the nipples removed.