Nylon Anchor Rivet available in 25mm & 38mm lengths25mm rivets available in grey & stone colour. 38mm in grey only.Used for securing 4mm bird posts and/or 4mm split pins into masonry surfaces.Shouldered design keeps moisture from entering hole and prevents freeze-thaw wear.Sold in packs of 100 rivets, required a 6.5mm diameter hole.DimensionsMushroom Head outer Diameter: 15mm.Max Height Above Surface Once Installed: 4mm.Hole diameter required in masonry: 6.5mmHole depth required in masonry: 25mm for PW209 & PW210 or 38mm for PW254.Usage25mm rivets can be used for seagull posts and pigeon posts when required to be installed on masonry substrates, they can also be used to secure counter-tension fixings including screw pins (PW211) and 25mm split pins (PW247)