wiper blade, 1966 C20, issues

[ciscorusty]

Hi - Purchased wiper arms / blades from LMC Truck.

Blades fit onto the arms, but they are VERY loose, and when I turn on wipers, the blade "falls over" onto it's side.

the OEM wiper arm has a flat end, with a small bump on it. the blades fit onto the flat end, and i can see the bump thru the hole in the blade.

To me, almost seems like it needs a SHIM to make it fit snugly.

Any help? If needed, i can snap a few pics and post.

thanks,

rusty