Ex. + photos :

"Curved Axial Entry Fir Tree Roots (CAEFTR)
Figure 1 below illustrates the design configuration of typical CAEFTR, consisting of fir tree root blocks to the blades which are inserted axially into mating fir tree steeple grooves on the disk head. Depending on the manufacturer and design of rotor, keyways are then utilised to lock the blades and prevent axial movement in service."
(http://www.bindt.org/downloads/2A1.pdf)

Cf. : http://www.eiffel-industrie-turbomachines.com/en/galerie-pho...