Plastic washers will not rust like metal. The rubber bungs fit securely into the holes, and when you tighten the bolts, they compress to create a snug fit. The rubber grommets in the kit have a threaded section that allows them to be inserted directly into the holes in the top of the toilet. When the screw is tightened, the grommet expands and secures itself into the hole without the need for a nut on the opposite side. Suitable for 14-19mm holes. Fits most standard toilets. Includes fixings for 2 toilet seats. Easy to install in minutes. Simply remove the old bolts, clean the area, and install the new bolts. Includes 4 soft plastic washers. When tightening the bolts, the washers compress into the holes. Avoid over-tightening to prevent the bolt from pushing through the washer. Screw Diameter: 5.7mm Length: 48mm Tube Nut Diameter: 18mm (thickest), 14mm Length: 40mm Washer Diameter: 14mm Color: Black Material: Rubber and metal Package Contents: 4 x Toilet fixings Note: This package includes only the items listed above. Other items are not included. Note: Lighting and monitor settings may cause slight variations in color. Measurement may vary by +/- 1-3cm.