Expandable ball is made of black rubber, with solid brass thread inside. White toilet fixings is made of nylon material, long screws and gaskets are made of stainless steel. Sturdy and durable, rustproof and corrosion resistant, better than most plastic fixtures.Put the toilet seat bolts in the toilet mounting holes. The rubber grommets have a threaded section so you can just push them into the holes in the top of the toilet pan and when you tighten the screw it expands and tightens itself into the hole, without the need of a bolt on the other end of the screw.Black Set: Expansion ball diameter: Approx. 18 mm/ 0.7 inch (unexpanded state). Length: Approx. 40 mm/1.57 inch. Screw length: 48 mm/ 1.89 inch. Metal washer diameter: 14 mm/ 0.55 inch. Plastic washer diameter: 28 mm/ 1.1 inch. Suitable for 14 - 16mm hole.White Set:Length: Approx. 37 mm/1.45 inch. Screw length: 43 mm/ 1.69 inch. Metal washer diameter: 13 mm/ 0.51 inch. Suitable for 14 - 16mm hole.CRMYB2L11