The 18" Adjustable Walk-on Lid Bracket with stainless steel base & support arm are designed to support all types of lids: aluminum, stone & concrete. Holes have been added to increase both rigidity & mounting options. These same holes can also be used to attach a bonding lug to the lid bracket. (Bonding lugs not included with this part). Lid should not be more than 2" longer then support arm.