Fueling & Injection - Russell Push-On Fitting

Can someone explain to me exactly how these work? Does the end cap thread into the fitting, and if so, how do you tighten it if it is on a fuel line. Sorry if this appears to be be a dumb question.

http://www.summitracing.com/parts/RUS-644120/

Yes, they do, don't have to be more than hand tight.