Blue Anchor™ Fastening Inserts - Blue Anchors are used whenever mechanical fastening to the wall is required. If mechanical fastening is required on one side of the wall, then only one (1) Blue Anchor is required per block. If mechanical fastening is required on both sides of the wall, then two (2) Blue Anchors are requied per block. Many residential builders opt for Blue Anchors on all interior wall surfaces at a minimum.