A jig is a work-holding device that holds, supports, and locates the workpiece and guides the one or more tools to perform a specific operation.
Fixtures are the work holding devices, which holds, supports and locates the workpiece but not guides the cutting tool to perform a specific operation.
Fixture is used for the convenience of fabrication of a job by welding which is set in this device so that it can be swiveled around 360 Degree as per requirement.
It is rigid enough for this operation
Usually drill jig is not clamped to the drilling machine table because, it is rigid enough for this operation.
V-locator is best suitable for location of a round shaped jobs.