The difference between a job-worker and a works-contractor can be derived from the nature of supplies they make. For instance, Job-work is defined as:
(68) “job work” means any treatment or process undertaken by a person on goods belonging to another registered person and the expression “job worker” shall be construed accordingly;
Works-contract is defined as:
(119) “works contract” means a contract for building, construction, fabrication, completion, erection, installation, fitting out, improvement, modification, repair, maintenance, renovation, alteration or commissioning of any immovable property wherein transfer of property in goods (whether as goods or in some other form) is involved in the execution of such contract;
By analysing the difference we can figure out that works contract involves process on an immovable property. Whereas job-work is mainly on movable property.