The thread protector that will work with the Griffin Armament Taper Mount Tactical Barrel Compensators can be found at the link below.
https://www.opticsplanet.com/griffin-armament-thread-protector-for-taper-mount-muzzle-device.html
Yes. This Griffin Armament Taper Mount Tactical Barrel Compensator will fit on your Sig 716 if you use the 5/8x24, .30cal model. MPN:TMTC305824
Griffin Armament does not make a version of this flash hider for 9mm. They do have a few other options including the Minimalist flash hider found here:
https://www.opticsplanet.com/griffin-armament-taper-mount-minimalist-barrel-flash-hiders.html?_iv_threads-per-inch=1-sl-2x28&_iv_parent-caliber=9mm-caliber&_iv_code=28N-BFH-GRI207-TMMFH91228&_iv_caliber-193146313=9mm-caliber
No. When using the Optimus with the Taper Mount Minimalist Blast Shield, the muzzle devices that will work in this configuration are the Paladin 2 Port Brake, Minimalist Stealth Flash Hider, EZ Brake, Minimalist brake (both the steel and titanium), and Direct Thread Adapter.
OAL = 2.2 inches per the Griffin Armament website