SF-90Q (Safety, FCD, 90 degrees throw, Q lever) is a non-ambidextrous (single sided) semi auto safety based on the ASF (Ambidextrous Safety, FCD). SF-90Q features a 90 degrees throw, and a Q (offset) lever. SF-90Q can be installed on the receiver with either the lever on the left side, or its right side.
Since ASF's introduction in early 2020, it's become one of the most reliable, compatible and popular AR15/M16 safeties. It isn't just one attribute, but the combination of the smooth rotation, positive detent engagement, no-wobbling levers from tight tolerances, Swiss CNC machined components and superior ergonomics.
If there was one area customers have asked for and we've heretofore not addressed, it is that not everyone wants an ambidextrous safety. ASF can be fitted with a cap on the side where the user doesn't want a lever, but the cap costs even more to make than a lever, a single lever ASF costs the same as an ASF with two levers. Economically, a non-ambidextrous version of the ASF makes a great deal of sense for those that don't need or want to use an ambidextrous safety.
Though SF-90Q is reversible, i.e. the lever can be on either side of the receiver, do note that Q (offset) levers are side specific. When ordering SF-90Q levers, the drop down menu offers either the right hand version with the lever on the left, or the left hand version with the lever on the right.
While a left Q lever can be installed on the right side and vice versa, the way the Q lever is offset will differ if a left Q lever is installed on the right side, or when a right lever is installed on the left side. The way the Q lever is designed to function on the ASF is with the offset biased towards 12 o'clock when the safety is on SAFE, but we've seen users do the opposite, where the offset is biased towards 6 o'clock, which is the way HK weapons safety levers are arranged. There is no wrong way as long as it works for the end user.
Left: ASF Q lever. Right: HK MR556/HK416 lever, notice the ASF's lever is biased towards the top, while the HK lever is off axis towards the bottom.
The Q lever is offset so on a 90 degrees throw ASF or SF safety, the lever is closer towards the rear (butt stock side) when the safety is on FIRE/SEMI, this offset allows most users to access the lever with their thumb without breaking their grip. For an ASF or SF with a 50 degree throw, the Q lever serves a different purpose. The Q lever is off axis towards the top when the safety is in the SAFE position, when rotated to FIRE with a 50 degree throw, the offset places the lever higher up, this has the effect of putting more distance between the lever and the user's extended trigger finger which can inadvertently / unintentionally lift and rotate the safety back to SAFE.
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