Oh my - aren't these beautiful?
They measure about 24mm and fit into the 25mm trays I sell - they are lovely clear glass and the novelty factor here is that they are flat! If the domed ones are not your thing, try these. They will be perfect for jewellery and magnets.
Just arrived in the shop, they sell at £3.00 for 10. Find them at the Jasmin Studio Crafts Shop.