Okey-dokey. This must be your first ship, eh?

The Concept has a DDF head which features individual flapping/feathering spindles, as opposed the more common solid through axle. These spindles are what support the blade grip bearings. If you were to remove the eight screws which secure the two halves of the rotor head, you would find that these spindles are held in there by a solid pin with a bushing on each side.

Removing the four additional screws that hold the halves of the blade grips together would reveal the bearing/spacer stack inside, all of which is secured onto the feathering spindle by a 3mm bolt in the outside end.

There a numerous ways to balance a head. Some are better than others, but the ones that work all require some sort of balancer, commonly called a "high-point". DuBro makes the only current one available, as far as I know.

I always check the head with everything except blades. That way I kinow that the flybar and paddles are right. If the head is right, and the blades are right (equal weights and CGs) then the blades will bolt right on without causing any shakes.

Concepts have two different types of blade grips. The early DX/SE/SX grips had 8mm spacing, requiring 8mm roots on the blades. These are now very difficult to come by.

The later SR series of machine had 12mm spacing, which is quite common. The Concept's problem is that it takes rather short blades; 530mm max for the latest iteration.

You said the blades had two washers. That leads me to think you have SR grips that somebody installed the old foamies or after market woodies (8mm root) on. Again, I can't be sure without seeing what you've got.

Steve