Important:The threaded stem size is 5/16"-18UNC x 1", Thread (US), the stud diameter of this wheel is 5/16",stud length is 1"(20mm), and it's imperial, not metric. It doesn't fit M8 pitch . Imperial 5/16"x18 TPI fits better.
Specification
Wheel Material:Polyurethane Rubber
Stem Diameter:5/16 inch (10mm)
Stem Length:1 inch (20mm)
Safe for All Floors: Working great for all kinds of floors including hardwood laminate, tile vinyl, stone, marble, concrete, carpet, rug and bamboo flooring.