This is kinda (but not really an odd size) and I really couldn't find anything in my candle or jar collection to fit it exactly, at least nothing that it screws onto. My guess is that it's made for popular jar candles like Yankee and Village but it's a tad larger than most of the other caps I've seen and would just rest atop the candle.
The inside diameter of the cap is about 3 1/4 inches like most candle jar caps but the threads in this one allow just that teeny tiny extra amount of room to maneuver (I'll explain below.)
The rusty cap rests on top of my Yankee candle comfortable with room under there to spare (it can jiggle around a bit.) A friend of mine and I have been hunting for caps that fit the off-brand candles such as the one in the photo below that I picked up for a song at the Christmas Tree Shop. As you can see from the photo, the off-brand candle has a thicker glass lip that doesn't permit most candle jar caps to go down over it.
With a wee amount of adjusting, this lid did indeed go down over the rim of the off-brand candle. It ain't a perfect fit but if you've been searching for something for the off-brand candles, this cap might just do the trick.
Anyhoo, enough of my problems (if candle caps were all I had to worry about...lol) and back to the item. We have several of these in stock and the rust pattern on each varies from the one shown in the photo. Some are streaky, some are blotchy but all are very cool. The candle jar cap comes new from JM Imports.