You can find the bead hole size in the product description for each item with a bead hole under 'More information'. When you order beads and stringing material this is of course very important to take into account.
Note: beads with a bead hole of 1 mm will (almost) not fit on stringing material of the same width. Always choose one or two sizes smaller to ensure that it will fit. Always pay attention to the type of stringing material you want to use. Elastic thread and metal wire are easy to thread. Wax cord and nylon cord are a bit more resistant and therefore more difficult to thread, unless the bead hole is large enough.