My wife has a Sparc 2 red dot on her Springfield Saint AR and the other day I needed to replace the cap and couldn't get it off, had to use pliers when I got home and I scratched it all to hell and back, then I couldn't get it back on, it wasn't cross threaded it seemed the cable tether that holds the cap on was way too tight and binding it up. Called Vortex and they said it is a known problem and some of the cables were sent out too tight from the factory, she said they will get me a box in the mail to send it back, and it is usually a 3 day turn around. Good to deal with a company that stands behind their product.