This is a measuring guide for shades that fit this description

If the holder does have screws, most likely it is an IES Glass Lamp Shade. IES Glass Lamp Shades are commonly used as reflectors for cloth lamp shades on floor and table lamps.

IES stands for Illuminating Engineering Society. It has been widely used by many lighting manufacturers and is one of the industry standards in photometric data distributionThe cloth lamp shade frame usually has indentations where the shade sits on the glass shade.