There are two types of flanges that can be used for this application. The most durable post-to-surface mounting attachment we offer is welded flanges for posts. Factory-welded, then powder coated, these durable, welded base flanges are ideal for mounting a post to hard surfaces such as concrete. They are sized appropriately for each type of post’s base and then welded to the base. For best results, use welded flanges when the surface grade is level or near-level. Shimming can sometimes work if the surface near level. Attractive skirt covers are available to conceal the weld as well as the bolts and shims used to secure the post to the surface. An alternative is our two-piece wedge flanges for posts. Though not as strong, they can be more versatile because they enable you to cut each post on location, which can be useful in keeping the top of the fence level when the grade below fluctuates. For a durable and versatile installation without the use of flanges at all, you may want to consider coring a hole into the concrete surface and installing your posts by re-cementing. Properly executed, this can be a very effective installation approach, but we strongly recommend you contract a professional concrete cutting company to do the coring.