It's M2.5x7.5mm with a 2mm thick head (total length 9.5mm)

MEASURE the screw that you intend to replace with it to see if it will fit. Clones vary ALOT. Some of the same model will have an M3 screw where others of the same model will take an M2.5. Lengths can vary depending on the positive insulator used. So when you are dealing in clones, don't trust someones word that it will work on X atomizer. They could be talking about a different SKU of the atomizer.