A welded chassis would be one unit. A bolted chassis would have cross members that are removable.
welded on
bolted in from new
Bolted on
because it is
Its welded.
I have an 87 Ranger and it is welded on.
The chassis is the structural elements of the vehicle. A unibody chassis, (no separate frame) includes everything but bolted on body panels. If the vehicle has a body bolted on a separate frame construction then the chassis is the frame.
They are bolted on
they are usually bolted on in the front of the converter.
It's bolted on the body, welded on the door. Door pin/bushing replacement guide: http://www.digitalrevo.com/jeep/doorpins.html
Direct replacements are bolted in and some aftermarkets are welded in.