The SBA4 has the rearward portion reinforced to enhance stability and comfort.  This brace works great for all AR-15 and AR-10 pistols.
 
Features
Designed after the SBM4™
5-position adjustable
Integral, ambidextrous QD sling socket
US veteran designed and proudly made in the USA
Product includes:  brace, 7075 mil-spec carbine receiver extension, adjustable nylon strap