Form f

Section 6A(1) in The Central Sales Tax Act, 1956Incase of manufacturer or trader the following will apply : Section 6A(1) in The Central Sales Tax Act, 1956

If a person sends goods outside from its state to its branch office in another state then it is not sale because you cannot sell goods to yourself. Similarly if a dealer sends goods to its agent in another state who stocks and sells goods on behalf of the dealer, such agent is called consignment agent and such stock transfer is also not considered as interstate sales since there is no sales involved in it, sales will take place when such agent will sell goods. But to prove such stock/branch transfer, F form is required to be produced as proof.

Since u r into purely service business u can use delivery challan (In TN Form-JJ is used) and mention that " The material is sent for Service purpose only not for Sale " 

Dharmendra