Drop Shank For Quality S Hitch

I need a 6" drop shank for a Quality S brand weight dist hitch. My question is, are the shanks interchangeable with different hitches? Will a Reese shank work or other brand? I called and talked to "etrailer.com" folks and the guy I talked to wouldn't say....other than each shank is designed for especially for each brand of hitch. I figure there was some kind of liability in him saying ..yes there all or most are interchangeable.