Brass Dish shaped washers commonly used in the Building and Insulation Trades.
The washers are approximately 25mm in diameter with 4.2mm holes across the centre line to accept plasterboard screws, cable ties or wire ties etc. The curvature has a depth of approximately 4mm.
These washers are made from 0.55mm thick pure Brass so that they are strong and will not rust or corrode in any environment.
