Rcm in gst for purchases only or for expenses also?

if company has a gst no and if purchase some thing for 

that concern company it is from register or inregister dealer no matter 

u have to pay gst on that 

As per Rule 9(4), whenever some taxable goods or services are supplied by an unregistered person to a registered person, Registered person is required to pay GST. There is no requirement that such supply must be for furtherance of business, mere supply is enough.