I lost my arsenal of discarded bulbs this year so I broke down and bought these as the bases looked identical to the bases in all my fairy lights. Of course they didn't fit. They were slightly too big for rosettes, about the width of a human hair. Looking at these and my old bulbs side by side, I couldn't tell the difference between the caps, but my digital calipers measured a difference of seven to eight thousandths of an inch, which was enough to keep the new cap from slipping into the socket. and stayed seated. I ended up replacing these new bulbs with the old sockets, a bit more work but the end result is the same.
Antique 40W T14 Incandescent Light Bulb With Medium Screw Base (E26) By Bulbrite
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