Each piece is printed out individually. Grooves are designed to allow the anvil catch to slide underneath filter.

The top cover snaps into place and allows for aggressive shaking without the components falling out.

The slide tongue and groove may have some filament that doesn't adhere properly, in my experience that isn't detrimental to the operation of the joint.

After printing, the joints need some breaking in. slide the tongue and groove joint together  and rub repeatedly until they slide smoothly.