Where to Use For use with masonry rivets to keep pigeons off ledges Product Specification Manufactured from 304 stainless steel 90mm Single headed post. How to Install Use with masonry Anchor Rivets Use at least 2 rows of posts to protect ledges Use 115mm single headed or 130mm double headed posts for the front row. Use 150mm single headed posts for the second row Use double headed posts for an extra level of protection Please note: This is a pack of 100 posts.