45mm Topcoat/Finish Brush (for sealers and smooth finishes). The 45mm Topcoat Brush is a very high quality lightweight brush, ideal for a variety of projects. The 45mm Topcoat Brush is primarily made of natural bristles but contains a light blend of synthetic bristles to lessen the opportunities for brush strokes. The 45mm Topcoat Brush was carefully designed with characteristics to help users limit the amount of product applied to a surface. This is a huge benefit when applying sealers such as Clear Topcoat Sealer or Clear Finish.