As others have said, the lightbulbs only fit OTT fixtures.
The OTT Lights themselves are worth 10 times what I pay for them in terms of SAVING MY EYES from strain and premature aging, matching colors, etc. I can do 8+ hours per day hand sewing or embroidery with an OTT light and never feel it. Also, they're terrific for reading (studying) and an absolute godsend for small-scale intricate work like beading or petit point embroidery.
I bought a flip-up Task light for my Mom for her 75th birthday a decade ago and she is STILL raving about how huge a difference it makes in her hand-sewing and crafts work. By her recommendation alone, over 20 of her friends in her various craft and social groups have bought OTT lights. (No, I don't work for them!!!)