New to me, at least. I've been looking through plugs to find the ones I want to use on my roadster. Most of them are the most common types, shown in the first two pictures.
The third picture shows the only plug out of several dozen that has a brass collar. I don't recall ever seeing one like it. Can anyone shed some light on this one?
That is earlier than the other two. Difficult to find a set of them.
I'm not sure what you mean by the brass collar, but the straight sided type was used up to about 1919. Then then the ribbed brass top. I have seen some of the ribbed type without the brass top, but don't know when they were made. Maybe between the two? Are the connection threads the same size as on the straight sided plug? The straight sided plug takes a #5x40.
: ^ )
The ribbed types are replacements for the type on the far right. My opinion is the ribbed ones were an over the counter plug, not used in production. I bought a lot of NOS ones with the ribs and they came in the light blue Champion boxes that were typical of the 1930's.
The brass tops replaced the type on the right in production, perhaps around 1922.
I have LOTS of early straight side Champion X plugs. Never seen one with a brass nut before - that is quite unusual. I don't have any opinion on that.