The Vortex flash hider uses a patented 15 degree, right hand helical flute design to eliminate muzzle flash. Used by US armed forces worldwide as well as US Dept of Homeland Security and law enforcement across the nation. Machined from ordnance grade 8620 steel and finished with a mil-spec phosphate. Designed not to loosen under sustained fire. Compatible with Smith Enterprise's quick attach/detach Direct Connect (DC) sound suppressors. This model features a pre-drilled hole, specifically designed for permanently attaching this Vortex by blind pinning and welding. This is perfect for building a 16" barreled upper using a 14.5" barrel with permanent attachment. Due to the design of the Vortex flash hider, no crush washer is needed to install this sight and it is not recommended that one is used. Notes:Compatible with the SEI Direct Mount.