I will never change a rear sight blade without at least 3 spare springs and plungers ready to use. As long as I have backup, everything goes great. Don't have a spare and either the spring or plunger or both are gone at the blink of an eye. Last time I ordered parts from Numrich, I got a dozen of each. Overkill, maybe but I'll never have a gun sit 2 weeks waiting on a spring to come in the mail.