Is probable that besides cartridge, that you will also want to specify the rifle - for example, 30-06 is same base (case head) as 8x57JS or 7x57 - but the stripper clips for different rifles likely going to be different. For example, a stripper clip made for 1903 Springfield for 30-06 cartridge, likely not going to fit well to a German made k98K, even though the "case head" will be the same size.
Some were made of brass, some were made of steel - either "in the white" or blued. Some have one "nub" on the side - some have "three" nubs, and so on. Has been my practice to get the stripper clip to fit the rifle - then find the correct size for the cartridge of interest. Was at least one Mauser rifle here that a former owner had filed out the stripper clip notch on that rifle - no doubt to be able to use Swedish stripper clips for 6.5x55, which were a different size. Back in the day, I believe specific stripper clips were made for use in specific military rifles - so can find some 7x57 made in Spain, or Germany, or Portugal, or Brazil - I believe most countries that used 7x57 cartridge also made the stripper clips for their rifles - no doubt some might swap to another?