I've experienced that these type of pumps can go to extreme pressures with little effort.
The pressure can easily exceed the limits of the materials used.
In my case, the checkvalve blew at about 1150 psi and launched the pumphandle at my face.
My upper jaw cracked loose from the rest of my face wich healed by itself BTW, ..
..one tooth chipped and the gums were stripped off my 4 front teeth.My upper lip was minced meat on the inside and the nut holding the pumphandle on cut into my cheek.
That startled me a bit...
I'm building a new one soon..

anyway, screw on fittings are the way to go.