These are G sclae, 1:24 brake wheels. These were originally intended as EXACT repalcements for those found on USA Trains cars, but can be used for a lot of other applications. They have a 1/16" hole in the base to fit onto the standard 1/16" rod for the brake staff. Due to their size, these are only available in the Frosted Acrylic materials. We offer these only in larger quatities of due to the way they are made and costing issues. In fact, 16 of these on one sprue costs less than 2 single ones!