Nylon Anchor Rivet available in 25mm & 38mm lengths.25mm 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.Usage38mm masonry rivets are generally only used as anchor rivets for 38mm split pins (PW253) when securing post & wire runs to vertical surfaces such as window reveals and end walls. Then slide the net back along the wire rope framework, drawing it to one end like a curtain.