For aluminum backplate: 5052 aluminum alloy with black anodized finish For stainless steel backplate: 11-gauge (.115 in / 3 mm) 304 stainless steel Weighs 1.7 lbs (770 g) All edges are beveled to protect the harness The 3 holes at the top of the plate offer variable height adjustment for air cell and cylinder mounting. In addition, a corresponding lower oval slot allows for lower band bolts that may be misaligned Slots at bottom for use with 1" or 2" crotch strap 3/8" accessory mounting holes along the sides and bottom There are 4 upper and lower slots to accommodate nylon cylinder bands so a single cylinder can be strapped directly to the plate. Having 4 slots provides stability and prevents cylinder "swinging" Hardware not included