I stumbled across 12 of these on eBay and have never seen or heard of them. What were they used for ??

Undercabinet lights. I remember Menard's used to sell fixtures that took these lamps several years ago (around 2009-2011) that took these lights. The fixtures are long since discontinued, however they are still sometimes used for aquarium lights. My friend's aquarium has one, it's really bright and looks nice and natural.

Thanks, these have a really weird base, almost like a 3157 automotive bulb. I never understood why they make things with proprietary fittings that become obsolete in a very short time.

Osram GmbH in Germany was the very first to bring this T2 FM fluorescent lamp format on the market in 1993/94 with 6W, 8W, 11W and 13W ratings. They run only on electronic ballasts.

I stumbled across 12 of these on eBay and have never seen or heard of them. What were they used for ??

Probably would fit a fixture like this
I figure if I ever need any lamps, eBay is where I'll have to find them..