This Wilson Combat TRMLOKAR1014 AR-10 M-Lok Handguard is designed to fit .308 AR pattern rifles with a 1-7/16-16" receiver thread (DPMS .30 Cal pattern). "High-Profile" / SR-25 / LR308 rifles with a pre-2009 "DPMS" / Knights Sr-25 Pattern. A "High-Profile" / SR-25 / DPMS receiver will measure approx .210" or 3/16" thick from the top of the receiver rail to the charging handle cut out. The Aero Precision M5 Upper is a DPMS high profile receiver and should work with this handguard.
My man asked how long it is, literally first thing, it's 14.6" according to wilson and I'm no expert.