To assembly you take a lot of m3 nuts and bolts, for the gripper you also need nylock nuts m3. To connect the horns of the servos to the parts you use little screws like 2x10mm (or 1,5x10mm). The "bearings" are connected with double sided tape on the back of the servo. The "bearings" are made of plastic (PVC in my case) so it doesn't have much friction.
The base is made of one servo with 12mm spacers with m3 screw tread in it and some washers. The bottom and top plate are connected with 45mm spacers and connected with m3 screws which are sunk in the wood. The servo horn is connected with some small screws like 2x10mm (or 1,5x10mm) to the servoplate.
The underarms are connected with 2x10mm (or 1,5x10mm) screws to the servohorns and the servo itself is connected with m3 nuts and bolts to the servomountplates. the servomountplates are stuck in the servoplate with a bit of a press fit. Also u could use some glue for extra support.
The upper arms are connected on the servo with 15mm spacers with m3 screw tread in it, as you can see in the pictures.
The wrist is also connected by a press fit and some long m3x30 nuts and bolts to secure the mini servo.
For more support to lift something you can add a 45mm m3 spacer between the 2 servomountplates and a 15mm m3 spacer between the upperarm parts. Then you could attach a spring (or two) between them.