Canik changed the shape of the lanyard loop hole in the SF/SFx backstrap. That affects the “plug” that holds a TF magwell in place. To deal with the change, TF has a pair of new “plugs.” The “A” model fits the original backstrap, the “B” fits the new backstrap. If you have a TF magwell and need a “B” plug, give us a call and we’ll send you one for free! (Switching to a TF custom backstrap also fixes this problem.)