You may need granite countertop support brackets since granite tops can weigh hundreds of pounds. These can be either functional, decorative, or both depending on your granite countertop installation. It's important to understand why you're using them before you choose which ones to use. Check out Granite Support Tips to get started.
Many builders and designers use decorative brackets to support granite tops and offset the downward pressure from people pushing or leaning on a cantilevered top. These brackets can be a real pain since you tend to hit your legs on them. They may look rather unattractive too.
A good alternative to decorative granite support brackets is to place a concealed plate or piece of flat 1/8 inch thick plate steel screwed and bolted to the top of the wall. You can drill holes in the plate for screws. For granite, use silicone to adhere the counter top to the plate. The steel plate also protects the stone from cracking.
You need solid support for stone tops. Here's a selection of handmade, wrought iron and steel brackets made throughout the US. Each is designed to support the weight of stone counters, but styled to compliment your kitchen . . . More Countertop Supports
Handcrafted in east Tennessee, not bought from wholesalers at two dollars a piece. 1/4 inch steel, not breakable cast iron, these brackets are not made like soup cans, cookie sheets, or trash can lids . . . Fantasy Steel
If your intention is to use corbels as a means of support underneath a countertop, the depth of the corbel you choose must be at least 1/2 the depth of the overhang which it will support . . . More Inviting Home Products
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In designs where your countertop spans supports, the length of the span (side to side as your facing it) should be limited to 24" for ¾" (2CM) thick stone and 36" for 1¼" (3 CM) stone thicknesses.
For designs where your countertop is cantilevered or overhangs the supports, overhanging portion should be limited to 6" for ¾" (2 CM) thick countertops and 10” for 1¼" (3 CM) stone countertops. The overhang should never be more than 1/3 of the depth of the countertop (front to back as your facing it). Cantilevered countertops exceeding these dimensions require corbels or leg support underneath the stone.
Note: Fragile stones may require corbels and supports that are spaced closer together and that do not allow as much overhang than the specifications here.